1974 ignition/charging system
 

Hello everyone, got a problem thats begining to make me pull my hair out. I have a 56 dodge pickup with a transplanted clip/318/auto, along with the electrical system from a donor 1974 valiant. Ive had 5 years of trouble free cruising, until last summer. MSD ignition quit working so I just disconnected it and ran the stock module. It started burning up coils, slowly at first. The first one I thought, coils go out, repace it. a month went by, burned another. Got progressivly worse until it burned them within 15 minutes of driving. Now it doesn't seem to enough spark to start the engine while cranking.A hot wire from batt. to coil it fires right up, take it off it stays running but rpm drops. While running if an accessory like the heater is turned on the fan speed drops down to almost nothing. I have replaced Batt,alternator/reg,ballast resistor,ignition switch,starter relay, ignition module, EVERYTHING except the starter. Anyone with fresh insight? One other thing, this morning I pulled a batt cable while running just to see if it died. It did, had the alt/reg checked and both are good. Bob

I wish I was there. Incredibly difficult to troubleshoot a hot rod with unknown wiring.

HOWEVER DO NOT EVER remove a battery cable from a running vehicle. This is an old wives tale I wish I could kill. It proves NOTHING, and generates a high voltage spike when you do this, which can "kill" things, and the newer the vehicle and the more electronics on board, the more "stuff" you can damage.

First thing is determine what the charging voltage is.

1 Charge up the battery, let it sit for at least an hour, and have it load tested with a "carbon pile" type battery tester. IF POSSIBLE use a hydrometer to read cell-to-cell specific gravity readings.

2 Actually measure running charging voltage. Target voltage is 13.8-14.2 You can stretch it out to 13.5-14.5, depending on temp. Read this with engine running "fast" simulate "low cruise."

Also check "voltage drop" across both the ground and hot side of the harness. Voltage drop can cause overcharging. With the engine running "low to medium cruise" measure these tests with the battery "up" (normalized) and first with all accessories off, then again with heater, lights on

Stick one probe of your meter, on low DC volts, directly onto the battery NEG post. Stick the other directly onto the frame of the regulator. You are looking for a very low reading, anything over .2V (two tenths) is too much. The lower the better. IF this is high, the ground between the battery/ engine/ regulator needs to be improved.

Now do the same check on the hot side of the harness. Stick one probe directly onto the battery POS post, the other probe as close as you can get to the regulator IGN supply. Once again, the lower reading the better, zero is perfect.

Without knowing how you have your ignition wired, this could only be a guess.

You running a ballast? I'd check voltage drop TO the ignition system KEY ON, ENGINE OFF

Stick one probe right at the ignition system "ignition voltage." If you are running a ballast, this means on the "key side" of the ballast, not the coil side. Stick the other probe on battery POS. Again you are looking for a very low reading. 1/2 volt is too much drop.

If you do not run a ballast, stick that probe on coil positive.

You may have multiple troubles. Are you running a "bulkhead connector" like stock Mopars did, or did you just stuff continuous wire directly through the firewall?

You run an ammeter or not?

The wiring harness came from the donor vehicle, that being the stock bulkhead connector. I will load test everything tomorrow. Thing is, I replaced everythingwhen it was burning the coils and the ammeter was showing slightly positive charge. all the sudden it shows slightly discharge and any extra accessory robs it of amperage. Even just running the engine for awhile runs it down, slowly. I was leaning towards the bulkhead connections. You mentioned the ballast, can I get away with not running it?

NOPE. If you are running a stock Mopar ECU you definately want to run the PROPER ballast resistor.

But since you are burning up coils is it possible it's wired wrong?

The truck got along fine 5 years no probs.In hindsight tho it started by overheating the msd ignition box 2 years ago. Bought another off craigslist and it ultimatly quit awhile later.That was getting expensive so I just used the stock module. It took 3 months but killed the Accel coil. Rapid decline after that. I didn't check voltage yet today but I did bypass the aftermarket ammeter and the accessories are functioning like they should. Tommorrow I will go for a ride and see if the coil warms up to much. I learn something new everyday, no idea that was a draw on the system.

The way you worded that I assume you mostly used MSD? You can indeed get by without a resistor on those, but NOT if you have a Mopar ECU All they do, basically, is "replace the points."