74 duster electrical problems

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big block

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Hello Guys.
I need some suggestions I'm at my wits end on this one. I have a 74 duster was a 6 cyl now a 360. Car was rewired 3 years ago with a painless wiring kit. Ran fine for the last 3 years. A couple of month ago I took it to the strip and after 5 trips down the strip it quit on the coast down after the run. long story short couldn't get it started. Had it towed home. On checking it had tripped a 70 amp breaker I have installed in the system and had burned up my ballast resister,electronic ignition my dash gages 2 of the tail lights the relay to the electric fan and some some other things.
Replaced the electronic ignition and resister ignition again. and gages. ran a bit and burned up the ignition again. Finally I found the voltage regulator burned up. Replaced everything again. New resister new electronics new regulator checked the coil coil ok. new relay for fan new alternator. Car started but sounded like the timing had jumped. It kicked back on the starter. Car ran like crap and quit again. New plugs and new plug wires and new rotor and cap this time. Volt meter jumps wildly also.
Any ideas? The only thing I haven't replaced is the coil and dist. both are only a couple of years old and car only sees a couple hundred miles a year. Thanks
 
My best guess, full fielding the alternator. Regulator not regulating alternator output. Where the short is that is causing this ? I suspect a wire got too much engine heat, melted the casing, shorted to ground. I used to see this from time to time on those 80s GM hotrods that had a huge BATT wire routed to their distributor. When that wire shorted to the intake bad things happened from engine bay to fuse box.
 
Very first thing is what is this 70A breaker that blows?

Next, after you get it running again, make sure to ADD some fuses to protect the ignition. I'm surprised you didn't get this done with the Painless re-wire, they come with "plenty."

And immediately measure the battery voltage when running. It may be overcharging badly. Is the battery bubbling over?
 
The 70 amp breaker is off of the starter relay which power everything. I have everything fused but the fuses in the panel aren't blowing.
I did check the voltage and it was 12.56 while running. My cooling fan was on and draws 19 amps so I assumed that was pulling the voltage down.
How do you check an ecu to see if it is toast and does anyone know what the resistance on the coil should be on the primiary and secondary. How much resistance should be on the distributor?


Thanks for the input.
 
Even though the wiring is now different, you need to download a shop manual from over at MyMopar. Several of those, by the way, came from this site

Resisance values for the coil and distributor pickup is in those. I would at least download the 72 and 73 manuals, they are a great reference, and the 73 manual contains the newer front disk brake info

It is disturbing that you are blowing that one big fuse, but not something in the panel. This either indicates a short that is not related to the panel, or that the fuses in the panel are way too large. One "big" thing that can cause a short such as that is the alternator

But since you seem to have burned up these items, I would lean towards they are over fused individually, or somehow got wire WITHOUT being fused.

The problem is, not knowing how the car is wired, I can only guess

Again, immediately measure voltage of the thing charging so you know "where that is."

So far as testing a Mopar ECU you can "jig" it up "on the bench."

You need a coil, the ECU and the distributor

Lay it out on the bench. Follow the diagram. Find the two distributor pickup terminals on the ECU. Hook them to the distributor

Hook the ECU case to battery NEG

Coil does NOT need grounded

Distributor does NOT need grounded.

Hook coil + to the power lead terminal on the ECU. Get a clip lead hooked there and let dangle. This is your battery "hot" when you are ready

Hook something from coil "case" to a probe for testing spark.

Hook up your power clip lead. Twist the distributor shaft while holding the test probe near the coil tower. The thing should make sparks

If not, unhook distributor. Take first one, then the other pickup clip leads, and "tap tap" ground them at the battery connection. Coil should make 1 spark each time you do so.

If not, try another coil. If that does not fix it replace the ECU

IF you hook it all up and it WORKS, then there is something AFU in the car harness. SUSPECT a bad ECU connector OR a bad DISTRIBUTOR connector
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This is all you need to test the basics of the ignition. You can easily test the ballast separate. A battery, the ECU, distributor and a coil, and of course some test leads

2ai0wsj.jpg


Below, the basic diagram for a 4 pin ECU

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Below, the wire for testing spark. I use my 12V test light. No, LOL the spark won't blow up the bulb

166lmj7.jpg


Below, the ground connection. ALL you need is one wire from batt NEG to the ECU case

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Below, the two distributor connections. In the car these are polarity sensitive, but for testing does not matter

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Below, the coil NEG connection

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Below, battery PLUS connection, one wire to this terminal of ECU and jumpered over to + side of coil

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Below, all hooked up and ready to test. Should produce sparks at least 3/8" and typically 1/2" long

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Below, distributor "one wire" test. I have removed the other distributor wire for simplicity. Take the bare connector end or this clip lead (the yellow) and with everything hooked up, ground it repeatedly. Each grounding should result in a spark (In this photo you need to hook up the ECU ground wire, I left it off for the photo)



vgitld.jpg
 
Step one.. Rip out the universal harness stuff, and replace it with something you can troubleshoot with known literature and practices....
 
I think having new wiring in these old cars is a good thing. But you need to make sure that everything is protected with a proper size fuse for to handle that circuit.

I am currently re-wiring one and also adding a separate marine fuse panel to protect things like the alternator, ignition switch circuit ,both fuse panel feed wires and any additional relays for lights, electric fans , etc.

Everything needs to be fused according to wire size capacity.
If you have things burning up they are not fused correctly.
 

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67 dart I really appreciate the instructions on how to test things. It will b Sunday before I get to test the icu. As for the guys saying to get rid of the generic wiring harness everything is wired according to the duster wiring skymatics. i have a cd of the 74 duster wiring harness that is 30 pages long and every wire is like the duster diagram.
I decided to bite the bullet and replace everything. The dist and ballast resister will be in tomorrow. Here is a list of parts I'm replacing if you can think of anything else let me know.
new
icu
coil
rotor
dist cap
ballast resistor (dual) 5.2 ohm on top) 1.2 ohm on the bottom going to ignition
new alternator
new regulator
I did find 2 wires on the alternator reversed
the green field wire and the blue field wire were reversed on the alternator.

Thanks Big block
 
The green and blue are not critical, "electrically." I'm sure when these cars were originally assembled, the people doing assembly hooked them up "just so" but electrically no matter

What would be far more important is finding what is causing the harness burning. These were POORLY fused originally. The underhood ignition circuit supplying, ignition, VR, and blue alternator field is one. This same circuit also supplied "other stuff" on some cars, electric choke if used, distributor retard solenoid, and carb idle solenoid
 
wow you do know your wiring diagrams. I saw the retard and high idle solenoids in the diagram but there they aren't in my system. I do have a new holly carb on the motor with electric choke that was put on about the time all this started, but I had a edlebrock on before with electric choke. I'm using the same hot wire as before. The choke has it's own ground built into the side of the choke mount. What should I check on the choke? I noticed the holly electric choke doesn't seem to warm up as quickly an the old edlebrock carb but it does heat up and open eventually. I'll disconnect the hot wire to the electric choke before I try to start it up with all the new parts.
Thanks Big Block
 
I might have misread what you meant. In your first post you were talking about the ignition / regulator "burnt up." Do you mean they failed, or that you are suffering damaged / melted harness wiring, or both?
 
Ok dart. I got it running. I guess it was the pick up in the dist. It registered .460 ohms that was less than 1 ohm and had a break in the signal when I turned the dist shaft when out of the car.
The new dist registered 464 ohms so I guess the old pickup was bad.
Now the alternator isn't working I don't get any voltage out of the big pos post to ground. So I'm off to auto zone for another alt and another new regulator. I guess somewhere during all this trouble and testing I damaged the alt.
Thanks Big Block
 
Darn well before you throw too many parts at it we can step you through some simple tests. These systems are easy to troubleshoot. I doubt you hurt the alternator, frankly. "Before you" bolt the new one on, post back and I'll step you through some easy stuff
 
Ok dart
The old alt checked out good. so I didn't have to purchase another alt. I guess the only thing left in the system is the regulator. The reg is grounded good and I checked the wires. The green on the bottom field checks good to the connector on the regulator. The other field wire goes to the ballast resister and back to the other voltage regulator terminal. How do you test an electronic voltage regulator?

Big Block
 
The way I do it is "test around it." Some may think my method is "around the bush" but here's the thing. it (for me) is always better to check wiring if at all possible "under load" which seems to do a better job of showing up bad connections than does resistance (ohm) tests

First, a simplified diagram of the charging system:

Dual_Field_Alternator_Wiring.jpg


Essentially what you have there is the "ignition run" (blue) feeding the VR IGN terminal and one of the alternator field terminals

The VR must be grounded.

The IGN feed to the VR powers the circuitry and also acts as a SENSING point.

The VR controls alternator output by "controlling the amount of grounding" on the green field wire.

So first check the IGN terminal of the VR or as close as you can get, everything hooked up, and key on / engine off. This voltage should be within .2--.3V of the battery.

Next, check "full charge."

You can remove the green field wire at the alternator, and ground that alternator terminal. Easy bring up RPM and battery voltage should rise. Depending on state of batt charge, it might come up a lot. Try to keep it below 16V

You can also check the VR harness wiring by starting with everything wired normal. Disconnect the BLUE wire this time at the alternator and ground it. Now pull the VR connector and devise a way to jumper around the two terminals in the plug. A couple of machine screws the right size will work.

Again, this should cause "full field. or full output.

If this works, hook everything back up and see what you have. "Work" the VR connector in/ out and check for corrosion. See what you have for charging voltage, with engine warm. If it's high, above 14.5, I would again check for voltage drop from battery to VR.

Another way, with engine running, is to check battery voltage. If it's high, check voltage at the ignition ballast wire coming from key. If this is "normal" (13.8--14.2) then the VR is OK and is merely suffering from low supply voltage-------voltage drop.

The other "fly" in this soup is poor quality modern day replacements. "It used to be" that NAPA "Echlin" or "Standard Blue Streak" used to be good stuff. Does not seem to be that way.

These VR don't fail very often. The one on my car is used OEM. The one I used to have on my old beat up Landcruiser (Mopar power) was the same USED one on there from 74 something to whenever I stopped driving it. Last time it ran, charged just fine. That regulator is probably an early 70's OEM and I still have it "somewhere."
 
Now the alternator isn't working I don't get any voltage out of the big pos post to ground. k

By this do you mean the big post is "low," 11-12V instead of 14? Or is it actually "zero" volts?

That stud should ALWAYS be hooked to the battery. If it has no voltage, there's a break in the wiring.
 
By this do you mean the big post is "low," 11-12V instead of 14? Or is it actually "zero" volts? That stud should ALWAYS be hooked to the battery. If it has no voltage, there's a break in the wiring.

Hey Big Block,
make sure the voltage regulator and both alternator field wires are connected when checking voltage at the big post on the alternator or battery. Also, double check your wiring at the firewall connector, especially the wires that go to the ammeter and ignition switch.
 
Hello Dart
Sorry I haven't been on line. The a/c went out at my house and I've been dealing with that.
I won't get to test the duster until after august the 12th. I'm leaving in the morning for Colorado on the motorcycles for a couple of weeks. If it's ok I'll get with you after I do the test when I get back.
I do appreciate the help.

Big Block
 
OK good luck. Just add to this thread when you get back. "In a previous life" LMAO I worked in HVAC /R, as well
 
Hello Dart
Well I'm back from the great state of Colorado. Enjoyed the trip but am tired.
Back to the duster. I ran all the test you suggested, the last test was grounding the field to see if the voltage regulator showed charge. I did and the meter pegged positive. So I checked all wiring for grounds and found none. Everything checked out so I threw on another new regulator just so everything would be totally new and there would be no second guessing. Car started and ran, voltage meter showed a plus charge of about 10 amps the backed off to zero. I also have a voltage meter in addition to the amp meter. It showed no volts. I shut everything down and disconnected the volt meter just to be safe. I removed the meter and checked it directly to a spare battery. It just barley registered 2 volts so I guess it was damaged in the shorting of everything. Leaving it out of the system for now. The only thing I haven't hooked back up is the tach. I'll reattach the green wire to the coil some time this week.
As of right now every thing works properly it runs and charges.
I appreciate the help you gave me. The diagrams and suggestions really saved a lot of time and gave me some direction.

Thanks
Big Block
 
You are welcome. Now that you are making progress you should make sure the charging voltage is correct. Check, running and warm, fast idle at the battery.
 
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