Voltage drop at ballast resistor

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Paladin06 said:
When you say dual resistor do you mean 4 pole? My car has the 2 pole resistor.
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Yes. Its two resistors. The 5.0 ohm resistor is to power the ECU.

To amplify on 'downstream'.
When the engine is off, or the alternator not producing power, the battery positive is the highest voltage. When a circuit is completed, power flows downstream from the battery.
When the alternator is producing power, its output terminal is the highest voltage, from there all power flows downstream to ground.
 
Ninety percent of the time you do NOT 'really' have a 5 pin ECU and therefore the 4 pin resistor is only "using" the coil side of the resistance. This is easily confirmed with the following test:

Turn key to "run" engine off. Ground your meter, and determine where the switch side of the resistor is. These are the two poles jumpered together, if you cannot see that they are the two terminals with the highest voltage reading

Now read one of the other two. One will be same as coil + because that is where it's connected. If it reads 6-9V that is "fairly normal"

If the 4th terminal reads "same as" the switch terminals, that is the ECU terminal and that shows there is NO CURRENT in other words the ECU is not drawing that terminal. In other words, nothing is connected to it.

Further, the old "points coil" resistor is wired to the coil in exactly the same way on electronic systems. If the ECU quits, or distributor, and the coil/ resistor/ wiring is OK, you can unplug the ECU, drop in a "points" distributor, hook the dist. wire to the coil NEG and go down the road
 
67Dart273 said:
Ninety percent of the time you do NOT 'really' have a 5 pin ECU and therefore the 4 pin resistor is only "using" the coil side of the resistance. This is easily confirmed with the following test:

Turn key to "run" engine off. Ground your meter, and determine where the switch side of the resistor is. These are the two poles jumpered together, if you cannot see that they are the two terminals with the highest voltage reading

Now read one of the other two. One will be same as coil + because that is where it's connected. If it reads 6-9V that is "fairly normal"

If the 4th terminal reads "same as" the switch terminals, that is the ECU terminal and that shows there is NO CURRENT in other words the ECU is not drawing that terminal. In other words, nothing is connected to it.

Further, the old "points coil" resistor is wired to the coil in exactly the same way on electronic systems. If the ECU quits, or distributor, and the coil/ resistor/ wiring is OK, you can unplug the ECU, drop in a "points" distributor, hook the dist. wire to the coil NEG and go down the road
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I have a two pole resistor and a four pole ECU. One blue wire on the resistor from the ignition switch and two brown wires out of the Resistor. The out position on the resistor is up from 4.5 to 5.5 after cleaning the bulkhead connector in engine bay and battery terminals. I also cleaned up the ECU ground points.
 
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Which way you working?
If working from battery, looking for drops, I tend check at the solenoid relay, then the bulkhead engine side. Then the next in sequence would be the ammeter. Because of easy access, I usually skip ahead to bulkhead out to resistor and then go inside to the ignition switch 'cause its in the dash.

Some depends on what loads are on. Remember it only drops when there is current flow. ECU on and coil will draw some current, fan or lights will draw alot.

I wouldn't unwrapp around the welded splice unless you have a reason to based on voltage drop before and after.
 
After the cleaning, what is the voltage on the run wire (blue at ballast resistor)? Is it close battery voltage now that everything is clean? If not, then I'd work back from there, cause you're already standing there. So check the bulkhead. then go in and check at the ignition switch if its easy. then the ammeter.
 
Mattax said:
Which way you working?
If working from battery, looking for drops, I tend check at the solenoid relay, then the bulkhead engine side. Then the next in sequence would be the ammeter. Because of easy access, I usually skip ahead to bulkhead out to resistor and then go inside to the ignition switch 'cause its in the dash.

Some depends on what loads are on. Remember it only drops when there is current flow. ECU on and coil will draw some current, fan or lights will draw alot.

I wouldn't unwrapp around the welded splice unless you have a reason to based on voltage drop before and after.
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The voltage at solenoid relay reads the same as the battery. The bulkhead connector male side reads the same as the battery and solenoid.
 
Mattax said:
After the cleaning, what is the voltage on the run wire (blue at ballast resistor)? Is it close battery voltage now that everything is clean? If not, then I'd work back from there, cause you're already standing there. So check the bulkhead. then go in and check at the ignition switch if its easy. then the ammeter.
Click to expand...

The voltage is 10.45 at the blue wire while 12.45 at the battery.
 
Paladin06 said:
The voltage at solenoid relay reads the same as the battery. The bulkhead connector male side reads the same as the battery and solenoid.
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Are you back probing the bulkhead or did you remove the connector?
Sorry if that's obvious, bt just want to make sure there is current flowing. Otherwise even a poor connection will read same as battery (see my explanation for voltage and curren earlier in the thread)
 
Mattax said:
Are you back probing the bulkhead or did you remove the connector?
Sorry if that's obvious, bt just want to make sure there is current flowing. Otherwise even a poor connection will read same as battery (see my explanation for voltage and curren earlier in the thread)
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I removed the connector.
 
Paladin06 said:
The voltage is 10.45 at the blue wire while 12.45 at the battery.
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Well, if it was me, I'd check the bulkhead next, and then whatever is easier working back to the battery -
It sounds like you are testing with engine off - ignition on so power is from battery. So using my '67 as an example, I'd check N, P, and Z. Understanding Charging Systems with Ammeter
Of course the cavities on your '72 will be different. Because these are easier to access, I would (and have) started there. Using those readings, decide where to look next. For example, if N and P both read 10.5 Volts and Z read 12.5 Volts, then the problem isn't at the ignition switch. Therefore it must be from main splice to ammeter to bulkhead inside at Z.
But, if N had read 10.5 and P was 12.4, then the wires to start switch, or the bulkhead connection at N must be where there is poor connections or shorting.
 
Paladin06 said:
The voltage is 10.45 at the blue wire while 12.45 at the battery.
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You really just have to "go down the path" and check each one. Also one "easy" way to "fix" this (workaround) so far as the IGN supply is to use the blue wire to trigger a relay and run the underhood loads off the relay. This relieves stress on the switch contacts, and gives the VR proper voltage to "sense"
 
Disconnecting that connector was something like disconnecting an air hose with quick connect fittings on it. If there's 60 psi in the tank, then there's 60 psi in the line. Doesnt matter if its a big line, or a long line. There is no pressure loss because nothings flowing.

It will get easier. Just start with the basics on volts and amps. That will help big time.
 
Mattax said:
'72 should be a dual ballast resistor. What is on your car?
The 5 ohm resistor has a wire going to the ECU - it will show a big voltage drop.
The 0.5 ohm resistor should have the wire going to the coil - it should not show nearly as much voltage drop.
One possibility is these are connected to the wrong resistors.
Another is that something in the coil or the ECU circuit is a drawing a bunch of current.

The drop to 10 volts from 12.5 even with the resistor's feed side (probably blue?, or blue with trace?) is something else. Power is going somewhere and its not the ECU or coil. See if disconnecting the alternator's field ground (green wire at the alternator) changes that reading. If not, try the field positive (probably blue?).
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OK, I performed the steps you suggested below:

The drop to 10 volts from 12.5 even with the resistor's feed side (probably blue?, or blue with trace?) is something else. Power is going somewhere and its not the ECU or coil. See if disconnecting the alternator's field ground (green wire at the alternator) changes that reading. If not, try the field positive (probably blue?).

With the green wire or blue wire disconnected I read 12.45 volts at the blue wire (disconnected) to the ballast resistor. when I connect the blue wire to the ballast with either wire at the alternator disconnected I get 10.45 volts at the resistor blue wire. Where do I go from here?
 
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Paladin06 said:
OK, I performed the steps you suggested below:

The drop to 10 volts from 12.5 even with the resistor's feed side (probably blue?, or blue with trace?) is something else. Power is going somewhere and its not the ECU or coil. See if disconnecting the alternator's field ground (green wire at the alternator) changes that reading. If not, try the field positive (probably blue?).

With the green wire disconnected I read 12.45 volts at the blue wire to the ballast resistor. :) Where do I go from here?
Click to expand...

Really does not matter "where it's going" (unless it's a short) it is still a drop. The VR power and alternator field are both supplied off the blue wire. so now backtrack from the resistor back to the battery. I already "wrote lots" on where to check above........bulkhead connector.......ignition switch.......etc......back to the battery

And again.........consider installing a relay fired by IGN1 to operate the IGN1 loads. Don't forget that drop in that circuit is what causes the VR to overcharge the battery!!
 
The drop in that circuit IS ADDED to the VR set point. Let's say the VR is correctly attempting to regulate at 14V nominal. Let's say you have a drop down to 10V at the resistor. That amounts to nearly 2 1/2 volts (from battery of 12.6 or whatever) This means the system (battery) will run at 14+2.5 SIXTEEN and a HALF volts!!
 
Totaly agree.

My point was understanding that opening a circuit means there is no flow in the circuit. Its possible to narrow where the resistance is in a circuit, but only if current is flowing. So with the bulkhead to the battery disconnected, the reading was battery voltage - but could have a just one strand of wire left. Connecting it, and turning something on verified that part of the wiring was OK.

So that's how I got to checking the three cavities in the bulkhead to narrow where the voltage is dropping.
 
Lets do this step by step.
Use this diagram or make one like it. Make copies and write on it.

Recharge the battery on a charger.
* For your own education, measure the voltage across the battery while charging.
Remove charger.
* Measure Voltage at Battery Positive, Alternator Output (Bat), and Bulkhead at Red Battery, Black Alt, Blue Run.

Turn Ignition Switch to RUN.
* Note current flow through Ammeter. Should be around 5 amps discharging (3-4 to alternator field, 1-2 to coil and ECU).
* Measure Voltage at Battery Positive, Alternator Output (Bat), Red Battery at Starter Relay, and Bulkhead at Red Battery, Black Alt, Blue Run.
* Recheck Voltage at Battery Positive.
* Observe ammeter. Write down any change from first turning on ignition.
Turn Ignition switch OFF.

Main_charging_wires_plus.png
 
^^I don't see this^^

I use a much simpler method. You are trying to find the SOURCE (which may be additive sourceS) of the drop

Hook one lead of your meter to battery POSITIVE. Extend the meter lead with a length of wire so you can "reach." This can be no 18, small wire. There is little current flow

Now access various points "as you physically can" in the PATH of the circuit

So if you work FROM the ballast TO the battery the drop readings should get less and less

Read at the resistor, key in "run." According to what the OP has posted this will be "a couple" of volts. It SHOULD be "a coupld" of TENTHS

Now read the blue terminal going through the bulkhead, both sides of the connector (ignition run) chase back to the ignition switch, ignition run, and power coming TO the key / connector. RIGHT THERE should show some change "I would think."

If not the next point is the "welded splice" which you cannot get to without pulling the cluster and untaping the harness so "skip it" for now

Next is the ammeter.

After that is the red terminals through the bulkhead

The readings should be less and less, nearly zero volts

WHERE THE DROP is happening is where the problem IS

Let's say "it is" the welded splice. Lets say you read the same (about) 2 volt drop at the ignition switch but the voltage drop "went away" at the black ammeter terminal

WHAT IS BETWEEN THE TWO?

A piece of black wire and the welded splice!!!!

==============================

Let's say the voltage drop still showed present at the black ammeter terminal (2v about), but the red terminal was OK (zero or much less, a tenth or two)

??? Now you have to be careful, because "bumping" or wiggling stuff could actually temporarily "fix" the problem. This is almost "worse" because it gets you onto a wrong track sometimes.

But what this just told you is that the problem is right there at the ammeter. It is either a bad wire terminal, loose terminal, or loose/ corrosion/ other inside the ammeter.

Quite frankly the TWO BIGGEST CAUSES in this particular case is the blue wire terminal going through the bulkhead, the ignition switch connector, and the switch itself

Also remember it is nearly NEVER a "wire." It is nearly ALWAYS a switch, or a connector terminal. RARE but has happened is a bad welded splice.

First one of those I found........was about 1972 in an apartment parking lot, in a friend's 68 RR. The ammeter had been jumping all around. I had the cluster and about half the dash harness torn down ........my first time doing so, and did not know where the splice was located WHICH I COULD SEE on the factory diagram. "He" (my friend) thought I was nuts. I was the hero after that day, LOL All it took was a great big Weller soldering gun

This is not the day we found this, but this is the car. This was at our RADAR shop on my day off. Don't remember who owned the shaker hood Cuda on left. Brown was a Poncho Ventura one of the guys I worked with. Next is my black 426 '64 Dodge. Next (facing) is Dave's 68 RR, this is the car that had the bad splice. At far right is my Limelight 70 440-6 RR

The 70RR itself had massive bulkhead connector problems "about then." I bored out the terminals for the ammeter and ran wiring directly through the connector. Both the original owner and I were radio amateurs, and we both had "gear" in the car

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That's why I boiled it down to a simple, do this, instruction.
What 67Dart273 has written is all good. After you get up to speed, it will make sense when you come back and read it over. I understand you're not there yet.

If there's any part of my instruction that doesn't make sense or isn't clear, let me know.
You will have to figure out which cavity in the bulkhead has the connectors for each of those lines.
If it's not obvious on the car, then look at the factory diagram in a service manual.
- Second choice is an aftermarket diagram like these MyMopar - Mopar Forums & Information - Mopar Wiring Diagrams 1972 to 1976
First try to trace them on the car itself.
 
Mattax said:
Lets do this step by step.
Use this diagram or make one like it. Make copies and write on it.

Recharge the battery on a charger.
* For your own education, measure the voltage across the battery while charging.
Remove charger.
* Measure Voltage at Battery Positive, Alternator Output (Bat), and Bulkhead at Red Battery, Black Alt, Blue Run.

Turn Ignition Switch to RUN.
* Note current flow through Ammeter. Should be around 5 amps discharging (3-4 to alternator field, 1-2 to coil and ECU).
* Measure Voltage at Battery Positive, Alternator Output (Bat), Red Battery at Starter Relay, and Bulkhead at Red Battery, Black Alt, Blue Run.
* Recheck Voltage at Battery Positive.
* Observe ammeter. Write down any change from first turning on ignition.
Turn Ignition switch OFF.

View attachment 1715165636
Click to expand...

OK, here's what I think I found.
Recharge the battery on a charger.
* For your own education, measure the voltage across the battery while charging. (13.24 volts)
My cars stay on a trickle charger all the time.

* Measure Voltage at Battery Positive (13.04 volts) *, Alternator Output (Bat) (12.96 volts), and Bulkhead at Red Battery (12.88 volts), Black Alt, (1.4 volts) Blue Run. (0 volts)

Turn Ignition Switch to RUN.
* Note current flow through Ammeter. Should be around 5 amps discharging (3-4 to alternator field, 1-2 to coil and ECU). (Yes I'd say 5 amps)

* Measure Voltage at Battery Positive, (12.10 volts) Alternator Output (Bat), (11.12 volts) Red Battery at Starter Relay, (12.22 volts) and Bulkhead at Red Battery, (11.81 volts) Black Alt, (11.47 volts) Blue Run (10.47 volts).

* Recheck Voltage at Battery Positive.* Observe ammeter. Write down any change from first turning on ignition. (No noticeable change)
Additionally I checked voltage at the back of the amp gage and it was 11.47 at both post.

While under the dash I sprayed contact cleaner into the bulkhead connector.

After I completed all the test, I checked the voltage at the blue wire on the resistor. It was 10.47. It is now 9.58. WTF???

Also I noticed the red wire at the bulkhead under the dash gets noticeably warm while making these test.

These numbers seem all over the map to me but with 3 back surgeries they are the best I can do.
 
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