Cranks but won't start. Unplug ground at field spade on Alternator and it starts?

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Dana67Dart said:
Without rereading the entire post ..

Have you verified that you have cranking g voltage to the plus side of the coil during cranking?

The IGN 1 is not active during cranking. And is a make before break type contact that gets power a spit second before the IGN 2 looses power.

If no IGN 2 getting to the coil it will never fire.
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Post #19 above has the voltage tests.
 
Just leave the alternator spade connector off. Thank me later. lol
 
Dana67Dart said:
That proves the IGN 2 is not providing battery voltage to the coil plus during cranking.

Why is the big question.
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If I unground neutral safety switch so starter won't run, disconnect Ignition 1 from ballast resistor, then put key in start position I measure 12.3 volts vs the battery 12.5 volts. Ballast is .8 ohms and I have another that is 1.2 ohms same behavior with both ballast resistors.
 
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Mattax said:
Probably within spec. Slip ring to slip ring the rotor resistance should be 3 to 4 ohms at room temperature. The carbon brushes work well as a conductor when spinning but can show a lot of resistance when measured with a meter like that. But at least we know it's not open.

Good. So no short there.

Good.

Assuming the old alternator has a grounded brush holder, that would eliminate something related to the grounding wire used with the insulated brushes.

And in a previous test it started when the grounding wire was disconnected.

So that seems to narrow it down to the section of the circuit. Maybe there's a short or partial short somewhere in there.
Next places to disconnect during starting are each end of the field wire (R3), at the VR, and then at the alternator.
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I added my Unilite wiring to the diagram you posted up. That distributor was installed around 2008, worked flawless until 3 weeks back at which time the module went into a slow death mode where engine stumbled/missed like a low fuel supply issue, ran fine when cold, would die when engine warmed up, and eventually car would start and immediately die. Also found electronic voltage regulator that had been on there 20 years or so also stopped working. This was several weeks back and why a new ignition module, new alternator, new voltage regulator, new ignition switch etc was installed. Usually when Unilites burn up there is an underlying issue causing it so I been doing voltage drop tests and ohming things out during the parts replacement. Car ran fantastic for two weeks then when I stopped to get gas last Friday the no start issue surfaced without warning.

Prior to the electrical issues that started weeks back the alternator, voltage regulator, unilite module, and M&H engine harness had been on there since 2008 and all worked perfectly. I had car apart last year and a half doing full floor replace and 6 speed swap engine kframe taken out ect. I did all that work myself. Car ran good for a couple months once put back together.....

Ignition Circuit.png
 
Thanks for the additional info. Now we all know what is on the car.
Sorry but at least I missed this part when I was responding the other night.
340sFastback said:
I do have Unilite distributor been on there for 14 years and it gets power for Ignition 1 side of ballast resistor. Unilite igntion module and MSD High Vibration coil mounted in stock bracket on manifold.
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Dana67Dart said:
That proves the IGN 2 is not providing battery voltage to the coil plus during cranking.

Why is the big question.
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That's what I would have first suspected - ign 1 & 2 wires might be switched
340sFastback said:
Ballast is .8 ohms
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Correct for points. Not sure what MSD coil and Unilite will work best with for street use.
340sFastback said:
then put key in start position I measure 12.3 volts vs the battery 12.5 volts.
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With points, the voltage drop from resistance in the line will only occur when the points are closed. And once its saturated the current will reduce. When the points are open there is no current flow through the coil, and with no flow, there is no resistance. So with no flow voltage is the same everywhere.
 
Mattax said:
Thanks for the additional info. Now we all know what is on the car.
Sorry but at least I missed this part when I was responding the other night.



That's what I would have first suspected - ign 1 & 2 wires might be switched

Correct for points. Not sure what MSD coil and Unilite will work best with for street use.

With points, the voltage drop from resistance in the line will only occur when the points are closed. And once its saturated the current will reduce. When the points are open there is no current flow through the coil, and with no flow, there is no resistance. So with no flow voltage is the same everywhere.
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The one test where I got 12.3 volts at coil the wire was disconnected from coil during that test.

The one thing I have not done yet is measure voltage to Unilite during cranking. Also note worthy is Unilite gets power from Ign 2 through ballast resistor when cranking. I tried moving Unilite power to Ign 2 side of ballast car starts sound like half cylinders are firing so moved it back to Ign 1 side where its been for 15 years.
 
With the new Unilite, it seems possible its power needs are more picky than your old one.
1720181796315.png

I've not worked with them, so all I know is what I've read in the instructions and things like that.
Its possible there is either internally different than your old one, or something about the wiring is reducing the power it needs to run during start.
 
340sFastback said:
The one test where I got 12.3 volts at coil the wire was disconnected from coil during that test.
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Show this to yourself with the water analogy.
Turn the garden hose on with the spray nozzle shut. Pressure in the hose is what? Same as the pressure supplied by the city or well pump.

Taking this further, connect the hose to a sprinkler.
The pressure in the hose when its running will be slightly lower but pretty close to house pressure.
Restrict the hose or supply (aerator in the faucet or pinch the hose).
That pinch causes a pressure drop when the sprinkler is running.
Shut the sprinkler off and what happens to pressure thoughout the hose?
 
Mattax said:
With the new Unilite, it seems possible its power needs are more picky than your old one.
View attachment 1716271967
I've not worked with them, so all I know is what I've read in the instructions and things like that.
Its possible there is either internally different than your old one, or something about the wiring is reducing the power it needs to run during start.
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Yeah it all worked great for two weeks, car would start so fast you did not even hear starter, car had never ran as good during that two weeks, then without warning no start issues arose when getting gas.

I will measure voltage to Unilite during start see what I get. And double check its ground wire. Also pull rotor out make sure module wires aren't rubbing rotor.
 
My thought is to test whether it relates to the Unlite's power feed by connecting the Unilite directly to the battery positive and then see if it will start. It can't be left like that because it will be powered with the key off.

Are you using a piggy back to make the power connection? Those are pretty conventient and make decent electrical contact.
 
340sFastback said:
This was the voltage regulator that had been on there for 20 years that died 3 weeks back and was replaced by the mechanical one from Napa:

Advance Auto Parts - Down for Maintenance

The local parts store says they can have one this afternoon.
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The NAPA VR32 has resistor's underneath? If you open it you'll see points. Very simple system.

I'm the last guy to tell you to buy parts and swap as a diagnoses method.
Have you tried starting with the VR ign side connected and the field terminal disconnected?
If it doesn't start then, that would seem to pin it on somethig to do with the VR.
 
Mattax said:
My thought is to test whether it relates to the Unlite's power feed by connecting the Unilite directly to the battery positive and then see if it will start. It can't be left like that because it will be powered with the key off.

Are you using a piggy back to make the power connection? Those are pretty conventient and make decent electrical contact.
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To wire unilite to Ign 1 I used a new Packard 56 female terminal at ballast resistor where Ign 1 and power to unilite in same terminal.
 
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I measured 6 ohms between voltage regulator and alternator field terminals. So released tab and pulled terminal out of plastic housing at alternator end, moved terminal around, saw 5-10 ohms as I moved terminal around then settled at zero ohms and stays there as I move terminal end around? Connection visually looks good. So it had excessive resistance now it doesn't? Open circuit between field wire and ground.

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Two week old voltage regulator resisters have burned appearance? With voltage regulator connected to Ign 1 and field wire disconnected car will start. Field wire connected and field wire now at zero ohms after wiggling alternator terminal end car won't start.

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Either !!!! There is some tremendous load somewhere during crank that is causing a massive voltage drop OR there is a bad connection in the brown / bypass circuit or bad ignition switch

You should be able to run this down quickly.

With everything normalized, measure the power at the brown/ IGN2 at the key switch connector, compared to the coil. If that is good, it almost has to be the bulkhead connector. This is a simple circuit. Goes from IGN2 at the key, through the bulkhead, and to the coil side of the ballast.

If that doesn't work I simply don't know "without being there."
 
Some of the isolated field alternators draw more field current than the original pre-70. Those resistors are gonna run hot, tho

The other BIG BIG BIG problem is that it is UNLIKELY that any replacement or rebuilt alternator actually meets the same specs that the OEM did
 
67Dart273 said:
Either !!!! There is some tremendous load somewhere during crank that is causing a massive voltage drop OR there is a bad connection in the brown / bypass circuit or bad ignition switch

You should be able to run this down quickly.

With everything normalized, measure the power at the brown/ IGN2 at the key switch connector, compared to the coil. If that is good, it almost has to be the bulkhead connector. This is a simple circuit. Goes from IGN2 at the key, through the bulkhead, and to the coil side of the ballast.

If that doesn't work I simply don't know "without being there."
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The brown wire inside car under dash at bulk head, in eng comp at bulk head, and at coil those voltage numbers match. I have not seen a voltage drop through that circuit at least from under dash bulk head to coil. That was the very first test I did, where I started.

I also ran jumper wire from battery to under dash brown bulk head wire. Car still would not start.
 
67Dart273 said:
Some of the isolated field alternators draw more field current than the original pre-70. Those resistors are gonna run hot, tho

The other BIG BIG BIG problem is that it is UNLIKELY that any replacement or rebuilt alternator actually meets the same specs that the OEM did
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I would think when Ign 2 gets power at ballast resister that some voltage flows through ballast to Ign 1 voltage regulator terminal and then to alternator field circuit during Start? Would that reduce volts to coil?
 
340sFastback said:
I would think when Ign 2 gets power at ballast resister that some voltage flows through ballast to Ign 1 voltage regulator terminal and then to alternator field circuit during Start? Would that reduce volts to coil?
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It should not if the wiring is up to it but this IS a source of voltage drop because of the bulkhead connector, quite often.

I am running out of ideas. I really have to lean towards finding a local guy who can take a fresh pair of eyes at the problem.

The same idea is true in "run" and I have posted this many times. The VR power connection IS the voltage sensing. Many old (??most??) Mopars have a voltage drop issue in the "run" position. In a stock wiring car, this can come from the ammeter circuit, the bulkhead connector, the ammeter itself, or drop in the ignition switch, switch connector, bulkhead connector and you end up with drop at the VR/ ballast junction. This drop causes the VR to ramp up and overcharge, AKA the reading at the VR/ ballast junction with IGN1 will read "fine" (14V) when running / charging but the battery will be HIGH.

Once again, I am starting to go round and round. Wish I was there. Bet we could find it
 
340sFastback said:
Two week old voltage regulator resisters have burned appearance? With voltage regulator connected to Ign 1 and field wire disconnected car will start. Field wire connected and field wire now at zero ohms after wiggling alternator terminal end car won't start.

View attachment 1716272039
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Since you have it off, remove the cover.
I don't think this is the problem but might as well visually check the fusible wires and points.

I'll need to reread later what you posted about the high restance when moving wire.
 
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