wiring harness meltdown..

[chargerdon]

Success...   sort of...  Band aid solution was to replace the 5 pin ECU with a new 4 pin...   

First...a big..big ...thank you to 734406PK...   he worked with me relentlessly in tracking down that the problem is a general voltage drop of about 1-1.5 volt thru my system not the ignition system wiring.  They reason it would start on run when jumpering the starter relay to start cranking is that the 1.5 ohm of resistance in bulkhead is eliminated to the ECU pin 1  ..it gets full voltage on run.   THANKS AGAIN 734406PK !!

Ok, one of the things i noticed in testing was that the ECU itself was consuming quite a bit of power.   So, even tho i was on a spare ECU which acted the same as the original...   I decided to purchase another new one.   This time a 4 pin ECU which would simplfy the wiring...ie. 5ohm resister side no longer needed with the 4 wire ECU.     

Putting in the NEW ECU (bought Masterpro brand at Oreilleys ($22.95) simply because it was inexpensive to try and was about the only one in stock at any of my local part stores).   Put it in and before even trying to start I measured the voltage at the brown wire with key in run...and it was about .4 volts higher than what it was with the 5 pin ecu.   Started the car via my relay jumper to make sure this ECU was even working...   Then tried the key start ...and HOLY COW...it started.   I guess that .4 volt gain was enough to cause the ecu to fire.  And starts quickly every time now.   So, this in itself is not a fix...but..luckily draws less power and therefore will fire from key.   

I still am going to pull the gauge cluster and measure voltage on the battery side of the amp gauge and the alt side of the amp gauge.   From all of my testing the probability is that the amp gauge getting old was beginning to put resistance into the circuit and maybe my harnsess meltdown...spiked it to be even worse.   So, will test this theory.   While i have it apart... tie the two amp wires together as the first step in the Amp Gauge bypass.   (ill buy a cheap cigarette lighter plug in voltage gauge for an interim solution to knowing if the charging system is working).   Later ill run the Alternator to Starter relay bypass.     

I read somewhere that Sunpro makes a voltmeter that can be bolted into the spot where the ammeter is located, inplace of our ammeter one wire then to ground.   Anyone know what Sunpro model it is and who sells it?

[Skid Row]

Sun Pro Model CP7985 is the one I think your referring to. Purchased one from Amazon just a few weeks ago, as I'm planning on doing the same conversion.

[fantum]

Just read this thread and had a similar thing happen to me on my old '87 van.  I was told (by an "old" mechanic) there are two "sides" to the ECU.  A "start" side and a "run" side, and one side operates independent of the other.  My problem was that I could start the van, but it would cut off as soon as the "start" side released.  I believe this may be why you were able to get it to start when you bypassed the "start" side of the ECU, and why replacing the ECU resolved the problem.

If the ECU had internal damage, this may have led to a number of the electrical gremlins you were experiencing when you were troubleshooting, and why you were misled throughout your troubleshooting process.

Just my 

Hope this is helpful.


MIKE
fantum

[chargerdon]

About 2 yrs ago i had a starting problem with my 66 Charger.   

It would "fire" from key and then die...  over and over.   Finally found the "run" wire wasn't making good contact with the ballast.   Cleaned put it back on ...and problem fixed.   

So, now i've had both.   I would love to chat with a Chrysler engineer...and ask them "why do you not send power over the Run wire" when cranking?   Without it the car has to start with a 1.2 ohm resisted ECU...   DUMB !!  Or maybe there is a valid reason..but...i sure cant think of one.   

[dodj]

   But,  If i disconnect both the choke heater wire, and the VR to take alternator off that amperage draw drops to about 3.6 amp.   So those two draw about 1.5 amp.   If i leave both of them off, the voltage rises and the car will start from key. 

The removal of 1.5 amps of load from your battery should not affect the voltage to any significant degree. The battery voltage probably does not change. You still have a high resistance connection somewhere in the start wire path. I suspect it is inside the cabin and/or BH connector.
The red wire supplying the battery voltage to the interior could be your culprit as well. Was it involved with the meltdown?

[chargerdon]

Dodj...Disagree...  1.2 OHMS not amps make a big difference in voltage.  Do a google search on OHMS law and you will see.   Yes, there is still a voltage drop somewhere...   I've ordered a voltmeter to replace the ammeter...  when it gets here ill pull out the gauge cluster and do some more investigating.

No, to the best of my ability to see with a flashlight to the drivers side of the bulk head, there isnt any visible damage to the bulkhead passenger side.   BUT, when i pull the gauge cluster i will be able to tell better.   

[dodj]

Maybe you misunderstood me.
What I am saying is the load you are talking about is not enough to cause a battery in good condition to loose the ability to supply you with 12vdc. So your supply is likely not changing so the voltage drop (caused by ohms that should not be there) is within the wiring. I believe we are in agreement. 
If it were me, I would check the red wire at the column connector while under load. Should be battery voltage. Or very close.
Next with the key in the start position I would check the start wire voltage at the column connector. Should be close to battery voltage.
If all is good I would move to the engine side of the B/H connector and check the start wire voltage there. You are loosing it somewhere. Just a matter of meticulously following the cct. Which can be time consuming...


P.S. I've been an electrician for 30 years....

[734406PK]

Maybe you misunderstood me.
What I am saying is the load you are talking about is not enough to cause a battery in good condition to loose the ability to supply you with 12vdc. So your supply is likely not changing so the voltage drop (caused by ohms that should not be there) is within the wiring. I believe we are in agreement. 
If it were me, I would check the red wire at the column connector while under load. Should be battery voltage. Or very close.
Next with the key in the start position I would check the start wire voltage at the column connector. Should be close to battery voltage.
If all is good I would move to the engine side of the B/H connector and check the start wire voltage there. You are loosing it somewhere. Just a matter of meticulously following the cct. Which can be time consuming...

You are spot on dodj! Chargerdon has already traced down the voltage drop to the passenger compartment and corrected a few resistances along the way. It is in between fuse link terminal 16 (interior) and the keyswitch feed wire, 1-1/2 volt drop. We suspect it may be the ammeter but the instrument panel needs to be removed for access.



P.S. I've been an electrician for 30 years....

[dodj]

Chargerdon has already traced down the voltage drop to the passenger compartment and corrected a few resistances along the way. It is in between fuse link terminal 16 (interior) and the keyswitch feed wire, 1-1/2 volt drop. We suspect it may be the ammeter but the instrument panel needs to be removed for access.

In the wiring close to the ammeter is a five way junction that may be worth looking at.

[734406PK]

Chargerdon has already traced down the voltage drop to the passenger compartment and corrected a few resistances along the way. It is in between fuse link terminal 16 (interior) and the keyswitch feed wire, 1-1/2 volt drop. We suspect it may be the ammeter but the instrument panel needs to be removed for access.

In the wiring close to the ammeter is a five way junction that may be worth looking at.

It carries the car's entire electrical load.

[dodj]

 

[734406PK]

 Any updates chargerdon?

[chargerdon]

The Sunpro voltmeter should be here any day...  will probably pull out the dash gauges this weekend...  and start the process of testing. 

Meanwhile, car is running just fine...   

[chargerdon]

Crap !!   Package arrived this morning...  It is a SunPro AMMETER..in the Voltmeter package...   sent email to vendor to resend the correct one.   Damn.. 

[734406PK]

Crap !!   Package arrived this morning...  It is a SunPro AMMETER..in the Voltmeter package...   sent email to vendor to resend the correct one.   Damn..

OMG they still make ammeters? Oh well, standing by