Turning key to "run" causes all power loss.

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dgebhardt

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My 74 Valiant had a faulty ignition switch (it wouldn't send 12V to the starter relay), so we replaced it with a new unit. That one was faulty from the start (you had to hold the key juuuuust right to get the starter to turn on), so we made arrangements for a replacement. I hooked up one of those handheld switches to the relay so that we could use the car. In the meantime, the new faulty switch began to cause other issues. The ammeter stopped working (it always reads 0A). But the car still ran. Then it didn't. The button would still turn on the starter, but the engine would never catch. I found that I had no spark. And only 0.3V to the positive side of the coil while the key was in "run". And then I found that none of the electrical items were working: blower, headlights, etc. I checked 12V at the battery, but only 0.3V on the wire going to the ignition switch. I disconnected the battery and suddenly I had 12V at the ignition switch again. But when I turned the key to "run" all voltage drops to 0.3V. I finally got the new switch and installed it today, assuming it would fix the issue, but it did not. I can let the battery sit for a few minutes, then disconnect it and reconnect it, and I will have 12V everyone again. But as soon as I turn the key to "run", I get nada.

I've tried:
1. Disconnecting all engine-side wiring that comes from the ignition "run" position: voltage regulator, alternator field connections, ballast resistor (both resistors), and ignition control module. This still gives the same voltage drop.
2. Probing the switch wires. I checked the switch operation. 12V source (red) to yellow and brown on "start". 12V source to black and blue on "run". 2 small red wires run to the key-in-ignition switch and are good. 1 orange wire provides illumination voltage to the lamp on the gear indicator. The new switches came with a small black wire that was not active on any positions. Not sure what this one is for. I taped it off.
3. Disconnected fuses. I disconnected 4 of the 7 fuses in the driver's side fuse box. Each fuse passed a continuity check. This still cause a voltage drop. I reinstalled those 4 fuses and removed the other 3 fuses. They likewise passed continuity and I still have the voltage drop issue.

Ideas for next steps?

I have the FSM for the 72 and 73 Dodge and Plymouth stuff, so I'll likely continue to use that schematic to move down the line. I assume that I have some sort of massive short and the battery (AGM) has some sort of fail-safe circuit breaker built in.
 
Have I talked to you about a correct 74 manual? I had a house fire, and had memory sticks from about 3 guys waiting on those files. If you need the manual, send me a pm, and we can arrange to get them to you by mail. They are too big to send over the net, at least from my end.
 
Go straight to your bulkhead connector, the big fat wire, I think it's black, and start at the fusible link, then the bulkhead, then the ammeter.
I can almost guarantee that's where yur gonna find the problem.
If you need to take the dash out, be sure to disconnect the battery first.
You cannot test the ammeter with an ohmmeter, you gotta pull some amps thru it.
If you decide to bypass the ammeter with a jumper, make sure the jumper you build is up to the task. What I did was put both wires on the same stud. and tighten the dickens out of it.
This left me without a charge indicator, so after every time I wind it up to 7200, I gotta check that the belt is still on, lol. I'm kidding. I mean I did that on the road to get home; then I fixed it.
 
67Dart273 said:
Have I talked to you about a correct 74 manual? I had a house fire, and had memory sticks from about 3 guys waiting on those files. If you need the manual, send me a pm, and we can arrange to get them to you by mail. They are too big to send over the net, at least from my end.
Click to expand...
I don't believe that I talked to you about a 1974 manual, unless it was over on the SlantSix forum site. In any case, I remembered that I had purchased a complete set of digital manual from Detroit Iron a few months ago and had not gotten around to downloading it yet. But I fixed that and now I have the schematics for the 74, which appear to be nearly identical if not 100% identical to the 73 schematic that I was working off of. But thanks for the offer!
 
A couple of thoughts on my next steps:
1. Measure the voltage drop across several sections of the wiring, to see if I have a bad connector. Ideally, I'd do this with the engine running (and high current flowing), but I can't start the ol' gal up as-is. I'll check the negative battery to several ground connections (engine, body, etc). I'll check the positive wiring through the starter relay, fusible link, ammeter, etc.
2. Remove either of the 2 ACC or RUN wires from the switch side of the switch connector. If there is a big short somewhere downstream, then disconnecting one or the other of these should help narrow it down. The dark blue wire goes out to the engine bay and powers all of the ignition circuitry. The black wire powers all of the internal items (lights, radio, blower, AC compressor, etc).
3. Get a heavy wire and run it from the battery positive all the way to the black or dark blue switch wires. This will bypass the connections at the starter relay, the fusible link, the bulkhead connector, the ammeter, and the ignition switch. If any one of those is causing the "short" then this bypass wire will allow me to start and run the car.
 
dgebhardt said:
My 74 Valiant had a faulty ignition switch (it wouldn't send 12V to the starter relay), so we replaced it with a new unit. That one was faulty from the start (you had to hold the key juuuuust right to get the starter to turn on), so we made arrangements for a replacement. I hooked up one of those handheld switches to the relay so that we could use the car. In the meantime, the new faulty switch began to cause other issues. The ammeter stopped working (it always reads 0A). But the car still ran. Then it didn't. The button would still turn on the starter, but the engine would never catch. I found that I had no spark. And only 0.3V to the positive side of the coil while the key was in "run". And then I found that none of the electrical items were working: blower, headlights, etc. I checked 12V at the battery, but only 0.3V on the wire going to the ignition switch. I disconnected the battery and suddenly I had 12V at the ignition switch again. But when I turned the key to "run" all voltage drops to 0.3V. I finally got the new switch and installed it today, assuming it would fix the issue, but it did not. I can let the battery sit for a few minutes, then disconnect it and reconnect it, and I will have 12V everyone again. But as soon as I turn the key to "run", I get nada.
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That wasn't good running with a switch that is wrong. Get the '74 manual and compare the switch and pigtails. Also compare with the original.
Assuming your on a computer, you can also use the search function for the forum. Its in the upper right corner of the screen. Search for 74 and 1974 within this sub forum (electrical). Also search for seatbelt interlock. The bypass is easy and done in the engine bay. Either push the button or permanently bypass as you'll find is generally recommended. The complications come with the control unit and the original routing. I suspect disconnecting under the seat may not have played well. I would think that would leave the start circuit open but haven't studied it.

An ammeter at zero means one or two things.
The needle is broken, its come apart (literally), or no measurable current is flowing through.
It should be zero when a car is running and the battery is fully charged.
It should have shown discharge while starting and charge after starting. Discharge with the engine off and dome light on.
If it has come apart, then there is no connection, or no good connection to the battery.

dgebhardt said:
2. Probing the switch wires. I checked the switch operation. 12V source (red) to yellow and brown on "start". 12V source to black and blue on "run". 2 small red wires run to the key-in-ignition switch and are good. 1 orange wire provides illumination voltage to the lamp on the gear indicator. The new switches came with a small black wire that was not active on any positions. Not sure what this one is for. I taped it off.
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Wire 12 ga Red is J1 (Ignition switch feed) It should always be hot.
Do the above search and you should find diagrams for '74 and possible connector drawings.

dgebhardt said:
3. Disconnected fuses. I disconnected 4 of the 7 fuses in the driver's side fuse box. Each fuse passed a continuity check. This still cause a voltage drop. I reinstalled those 4 fuses and removed the other 3 fuses. They likewise passed continuity and I still have the voltage drop issue.
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Off the top of my head '74 has nothing critical for running the car fused.
Voltage drops are caused by two things. Current flow rate and resistance. Voltage drop occurs when high current is flowing through some resistance, or low current is flowing through high resistance. V = I x R
Continuity only reveals that current flow is possible (there is a connection, but it may or may not be a good connection)
 
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This post shows the main feeds for the standard '74 wiring. Heavy duty alternator and rear defrost grid cars are a little different.
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1974 Duster total electrical failure, followed by quick recovery.

Hi All: Just had this happen today. After shutting off my engine (225 auto), the entire car went completely dead. Nothing. Having seen this before on another Duster, I immediately located the main battery feed connector behind the brake booster. This is a heavy gauge red wire with a...
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Thanks for the help so far. Here's an update:

I performed the voltage drop test and I found an issue. With the key off, I got a 0 voltage drop from the battery to the alternator, which should cover the whole circuit. However, when I went to each of the components (relay, fusible link, bulkhead, ignition switch), they were all zero except for the fusible link connection, which registered about 0.001 to 0.006 VDC drop depending on how I moved the wiring around. I then moved the key to the run position and did the same thing. Battery to alternator was 0.6VDC, which I feel is probably high. I could hear the blower running, but then it stopped. Checking the battery to the ignition switch and my voltage drop was 11.99VDC (my battery was slightly drained through all of this). Walking my way down the wire from the battery, the relay was 0VDC drop, the battery-to-fusible link connection was warm to the touch, and jiggling it around caused the power to come back on (the blower started up again). I looked at the connection and the 8AWG wire inside the connector was holding on by a couple of strands of copper and it looked burned. The connector on the fusible link side looked a bit melted, too. I think I found my poor connection.

My intent is to run all new wiring from the relay to the interior.. I will also replace the fusible link with a 40A maxi blade fuse. And, while I'm at it, I'll pop a grommet through the firewall and solder/splice the power wiring into the interior and up to the ammeter. Or, it may be easier to just run the 8AWG wiring up to the ammeter and just abandon the old power wire. I'll use all new OFC 8AWG wiring and soldered connections. I assume that the bulkhead connector is likely burned and corroded based on the visible appearance. I tried to depin the bulkhead connector but was unsuccessful.
 
It's probably not necessary, but I've gotten to where I bypass the ammeter (bolt one lug directly to the other) during any diagnostics at all.

Whether you leave it like that is up to you.
 
How much current, if any, went through wires for the volt drop test from the battery to alternator?

If your car has 8 gage wire, then it has the 'fleet' or the optional heavy duty wiring that came with rear defrost grid cars. The charge path is a bit different for each of the three possibilities. Lets try to establish which of these the car has before trying to pinpoint the problem location(s).

Posting photos will make it easier for us to help.
 
Mattax said:
How much current, if any, went through wires for the volt drop test from the battery to alternator?

If your car has 8 gage wire, then it has the 'fleet' or the optional heavy duty wiring that came with rear defrost grid cars. The charge path is a bit different for each of the three possibilities. Lets try to establish which of these the car has before trying to pinpoint the problem location(s).

Posting photos will make it easier for us to help.
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During the initial key-off voltage drop test, I'd assume that nearly zero current was flowing.

Switching the key to "run" caused the blower fan to come on (it was set to Lo speed) and possibly the interior lights (driver's door was open, most of the lights have LED bulbs in them, so low current there), plus whatever quick in-rush of current to the ignition coil. All said, the current was fairly low, but I quickly found the hot spot going into the fusible link. I'm still waiting on my wiring and parts (should be here today) to complete the rewiring. Then I can proceed with the voltage drop test (again) and I'd like to include turning on the headlights.

I do not believe that this car has the rear defrost grid. At least, I don't see the horizontal lines on the back glass that I would expect to see. In my inspection of the schematic and this car's wiring, I haven't come across the indicated wiring that would lead me to believe that this car was ever equipped with the defrost grid.
 
dgebhardt said:
I do not believe that this car has the rear defrost grid. At least, I don't see the horizontal lines on the back glass that I would expect to see. In my inspection of the schematic and this car's wiring, I haven't come across the indicated wiring that would lead me to believe that this car was ever equipped with the defrost grid.
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Those are the two options I know of where 8 gage wires were used.
Here's one version showing the feeds going through a gromment on the firewall.
1725908906936.png


The heavy duty wiring versions with rear defrost grid often used the alternator side of the ammeter as a junction post. So another visual clue there.

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Have you ever seen any Dart, Valiant, Demon or Duster with a rear window defroster?

I had a 74 4 dr. Valiant Brougham that had the factory grid type. It's funny that you mention it, but I think ALL newer cars have them but hardly anyone uses them. They're like turn signals, it's just too much trouble to flick a switch to turn them on! :mad: I use the one in my 2015...
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dgebhardt said:
During the initial key-off voltage drop test, I'd assume that nearly zero current was flowing.
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With no current flowing there will be no voltage drop.

To do a voltage drop dest we need to turn something on with a known (or measureable) current.
The difference in voltage from the power source (or any point in the flow path) to another point in the flow path will only occur if there is resistance to the flow.

No flow, no resistance.

So if the engine is off, our power source is the battery, and the battery feed has an ammeter on it.

Then if we want to measure voltage drop from the battery to the main splice (standard wiring), we can turn on the headlights - that's about 10-12 amps with the marker lights included. A glance at the ammeter will confirm that.
Then measure the voltage drop from the battery positive to the main splice. The wire from the main splice to the alternator Batt terminal has no current flowing in it so we can use that as an extension of our test probe.

1725910818192.png


Anyway the main point is that any voltage drop test must be accompanied by a known or reasonably estimated amount of current flow.
V = I x R

Use this method (voltage drops) to look for resistance that can not be measured be a typical handheld resistance meter. If you can measure it on meter, or see damage visually, then you don't need to do this sort of investigating
 
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Mattax said:
Those are the two options I know of where 8 gage wires were used.
Here's one version showing the feeds going through a gromment on the firewall.
View attachment 1716301141

The heavy duty wiring versions with rear defrost grid often used the alternator side of the ammeter as a junction post. So another visual clue there.

[/URL]



With no current flowing there will be no voltage drop.

To do a voltage drop dest we need to turn something on with a known (or measureable) current.
The difference in voltage from the power source (or any point in the flow path) to another point in the flow path will only occur if there is resistance to the flow.

No flow, no resistance.

So if the engine is off, our power source is the battery, and the battery feed has an ammeter on it.

Then if we want to measure voltage drop from the battery to the main splice (standard wiring), we can turn on the headlights - that's about 10-12 amps with the marker lights included. A glance at the ammeter will confirm that.
Then measure the voltage drop from the battery positive to the main splice. The wire from the main splice to the alternator Batt terminal has no current flowing in it so we can use that as an extension of our test probe.

View attachment 1716301154

Anyway the main point is that any voltage drop test must be accompanied by a known or reasonably estimated amount of current flow.
V = I x R

Use this method (voltage drops) to look for resistance that can not be measured be a typical handheld resistance meter. If you can measure it on meter, or see damage visually, then you don't need to do this sort of investigating
Click to expand...
I mostly agree, and I hope you don't take this as a criticism. On the contrary, I greatly appreciate your help. It wasn't until I made my original post and received the first round of suggestions that I remembered how to do a proper voltage drop test. :thankyou:

The voltage drop test assumes that resistance increases at the point of failure while under load. The magnitude of the load will proportionally increase the resistance. This is a critical assumption in this test framework. I could, for example, take a 1/8 Watt 220k Ohm resistor and add it in series with my tester probes. I would measure a significant voltage drop, but the current would be miniscule. If I had a megger, I could likely identify the source of failure just like the current-on voltage drop test, which you point out in your last statement (most meters can't do load-based resistance measurements); certainly my Fluke 111 can't. I only mention this in case somebody many months from now searches this forum and comes across this thread.

Regarding your attached photo, while I don't have the grommet on my firewall, it is the connector on the red wire that's touching your thumb that's failed.
 
Explain to me how you are going to find a low resistance drop point with a megger. I have been failed "little" by drop tests. You don't really effin care about proportionate increases or anything else. You are mostly just concerned with an unreasonable drop, and usually the really guilty culprit becomes fairly obvious. This can be helped greatly by "wiggle" tests. Wiggle the key, wiggle the connectors, wiggle any terminals, and just plain shake the living **** out of parts of the harness.

Sometimes it's helpful to add load artificially, I used to have a small carbon pile meant for generator work, not a huge 500-1000+ meant for battery/ starter testing. So if you had a problem in a lighter circuit, like the ignition circuit, you could artificially add "overload" and not really hurt anything--if you are reasonable. Also, in modern times, things I did not previously have, are such things as a temp gun for hunting hot spots
 
67Dart273 said:
Explain to me how you are going to find a low resistance drop point with a megger. I have been failed "little" by drop tests. You don't really effin care about proportionate increases or anything else. You are mostly just concerned with an unreasonable drop, and usually the really guilty culprit becomes fairly obvious. This can be helped greatly by "wiggle" tests. Wiggle the key, wiggle the connectors, wiggle any terminals, and just plain shake the living **** out of parts of the harness.

Sometimes it's helpful to add load artificially, I used to have a small carbon pile meant for generator work, not a huge 500-1000+ meant for battery/ starter testing. So if you had a problem in a lighter circuit, like the ignition circuit, you could artificially add "overload" and not really hurt anything--if you are reasonable. Also, in modern times, things I did not previously have, are such things as a temp gun for hunting hot spots
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You are right about my megger comment. My grognard maintenance guru assumed that I wanted to supply high voltage to find resistance (which is what a megger does) when I really wanted to simulate a load and test for resistance (aka voltage drop). Kudos to you and apologies from me.

I keep getting ads for one of those phone-mounted FLIR cameras for hunting for hot spots, but I haven't pulled the trigger yet.

In any case, the wiring, grommet, and fuse holder arrived yesterday. I'll try to find some time in the next couple of days to rerun the wiring from the starter relay to the ammeter post.
 
dgebhardt said:
I have the FSM for the 72 and 73 Dodge and Plymouth stuff, so I'll likely continue to use that schematic to move down the line. I assume that I have some sort of massive short and the battery (AGM) has some sort of fail-safe circuit breaker built in.
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Before going too far, track down the initial probem.

I've not seen an AGM with a built in breaker. I can say from experience that they do not like high charging rates. They get hot and stay hot (because the liquid is captive in the matting) when charged at 20 amps or so for 15 minutes. Bottom line with a severely discharged battery use a battery charger not the alternator if possible especially when dealing with an AGM.

20 amps for 15 minutes is a bit much for 16 gage wire at the crimp. Even the heavier terminals and wires may get hot.

Side note: '67 FSM says a voltage drop of .3 V is max allowed between the alt and the battery for a 10 amp current. My point is that even the factory knew there was resistance in the circuit with the distance in the engine bay, all of the junctions and the fusible link. I suspect it is why the alternator feeds directly to a welded splice with the only connectors being the ring terminal at the alternator and the push-ons (Packard 56/58) at the firewall. (In 1975 they split the feed through the firewall to reduce the maximum load on the connector. Heavy duty alternator optioned cars also split the load)

Short to ground. The only protection on a '74 was the 16 ga fusible link.

With the '74 seat belt interlock there are a bunch of wires going to the control unit including a start wire from the key switch. I haven't studied the details but its possible the loose connector and cable could be grounding out when the key is in start.

IIRC '74 also has an 'engine connector' to ease factory engine installation. R6 may even go through it (and if so that would make my statement in the side note innaccurate for '74). These are often a problem location as can be the steering column connectors.
 
Mattax said:
Before going too far, track down the initial probem.

I've not seen an AGM with a built in breaker. I can say from experience that they do not like high charging rates. They get hot and stay hot (because the liquid is captive in the matting) when charged at 20 amps or so for 15 minutes. Bottom line with a severely discharged battery use a battery charger not the alternator if possible especially when dealing with an AGM.

20 amps for 15 minutes is a bit much for 16 gage wire at the crimp. Even the heavier terminals and wires may get hot.

Side note: '67 FSM says a voltage drop of .3 V is max allowed between the alt and the battery for a 10 amp current. My point is that even the factory knew there was resistance in the circuit with the distance in the engine bay, all of the junctions and the fusible link. I suspect it is why the alternator feeds directly to a welded splice with the only connectors being the ring terminal at the alternator and the push-ons (Packard 56/58) at the firewall. (In 1975 they split the feed through the firewall to reduce the maximum load on the connector. Heavy duty alternator optioned cars also split the load)

Short to ground. The only protection on a '74 was the 16 ga fusible link.

With the '74 seat belt interlock there are a bunch of wires going to the control unit including a start wire from the key switch. I haven't studied the details but its possible the loose connector and cable could be grounding out when the key is in start.

IIRC '74 also has an 'engine connector' to ease factory engine installation. R6 may even go through it (and if so that would make my statement in the side note innaccurate for '74). These are often a problem location as can be the steering column connectors.
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The battery was failing to turn the engine over Saturday morning after several attempts to start, so I put it on my Schumacher smart charger (AGM mode) on Sunday and it was reading 100% charge by Monday evening. It was likely ready long before then but I didn’t check it since I knew that I didn’t have the new wiring stuff yet.

I agree with the AGM and breaker. I only mentioned that because when my household GFCIs trip, the voltage at the outlet is in the low single-digit or double-digit range rather than at zero or at full 115-120V. It was odd that I could measure 0.3-0.6V at the ignition switch, hence my thought that a similar safety switch had kicked in.
 
The new 8AWG wiring is in, along with a 40A in-line maxi-style fuse. A punched a hole in the firewall near the existing pass-through for the hood release cable and used a grommet to secure the wire. The wire terminated at the ammeter. The old cable was removed from under the hood and all the wiring received new wrapping. She started right up after all of that was done.

However, while buttoning up the dash and ignition switch wires, I found that the car would stall if the connector was bumped. Obviously, that's another loose connection. The black wire (from the ignition switch to the alternator) was also warm at the connector. I performed another voltage drop test and the hot side of the connector (red wire) was 0.35V drop from the battery, so I depinned the connector and tried to clean it and reinstall it. The voltage drop at the black wire was the same, so I started with the red wire first. The stalling issue was still there, so I simple cut the wire and added a single-line connector to the red wire and the black wire. The voltage drop went away, but the car would still stall if the connector was touched just right. Next, the brown wire was cut and a single-line connection was made. The stall issue was still there, which didn't make much sense to me, since the black and brown wires are the current-carrying wires while in the "run" position. And since I was already halfway to removing the entire 8-pin connector array, I just cut the remainder of the wires and added new connectors. My stalling issue is gone, but the wiring is a bit less tidy.
 
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