Electrical load problem

[Gryzynx]

I'll add my 2 cents worth here. If your engine dies immediately when you turn on the heavy loads, it is not going to be your alternator or battery. It will be a voltage drop due to bad connections. Here's what I would check for;

Measure your battery voltage directly across the battery terminals. Note I said the terminals, not the clamps. Applies for both + and - posts. Should be about 12.5V without the engine running and 13.5 to 15 with the engine running and the charging system working.Make the same tests with heavy loads, (headlights, heater motor on). Readings should drop slightly. If you are dropping 2 volts or more, suspect the battery, but I expect this will not be the case in your situation as you can start the engine and cranking the starter is about the heaviest load you can encounter.

Measure the voltage at the common side of the ballast resistor. It should be within a volt of the battery voltage. Keep in mind I'm talking about the common side, the one connected to ignition power, not the single wires connected to the coil or pin 3 of the ignition module. Also, make sure the case of the module is electrically well connected to the chassis of the car. Test by measuring voltage from the - battery terminal to the case of the ignition module. Should be 0 volts. If anything does not measure up, dig out the wiring diagram and start troubleshooting. You can verify that a bad ground would be fixed by running a temporary jumber from the case of the ignition module to the battery - post. Same idea can be used to verify a problem with primary + power. Jumper the common terminals of the ballast resistor to battery + post. You will not be able to shut the car off with the key, but it should also not die when you turn on the loads.

You can find some good info at this site.
http://www.allpar.com/fix/electronic-ignition.html

 

[Gryzynx]

Hmmm. Having some posting problems here. My apologies if this appears twice.

If you can start your car without boosting the battery, it is very unlikely that the battery will be the cause of the engine dying with electrical loads turned on. Similar thing with the alternator. Your car should run till the battery dies if the alternator is not working. This would take more than a few minutes to happen. Cranking the starter is probably the single biggest load you can put on your battery and the alternator does not kick in until the engine is turning at least a few hundred RPM, how would the car ever start if you relied on alternator output alone to supply ignition?

Much more likely is a voltage drop between the battery and the ignition module. This can be checked by measuring the voltage between the + battery terminal and the common point of the ballast resistor. Red lead of the meter to the battery + post and black lead to the ballast resistor common point. Take note that the common point is NOT the wires going to the coil or to pin 3 of the ignition module. If you see more than a volt, or if the voltage goes up when you turn on the heavy loads, dig out the wiring diagram and start troubleshooting. Make the same check on the negative/ground side of the circuit by checking from the battery - post to the case of the ignition module. You can verify a cure by temporarily running a jumper from battery + to the common point of the ballast resistor. (classic hot wiring). Same for a fault in the - or ground circuit. If you now can turn on the heavy load accessories without killing the engine, you know the problem is in the wiring.

 

[2 Darts]

I had a problem with the 73 sort of like this. Things just got dim, car didn't die. The components checked out fine. As much as I detested doing it, a weekend spent cleaning out the bulkhead connectors with contact cleaner from an old school electronics shop (used 2 cans) turned out to be the best investment I could have made.

Like 67GTX, I added up the electrical loads and found I can't run a 1000 watt power amp because it draws too much power. The 46 watt alternator can't handle it.

 

[Sinister.]

I pulled the bulkhead connectors off today and found a rather nasty surprise... nearly half of the alternator wire contact was solid white from corrosion. I cleaned up all of the other contacts and pulled the alternator wire from my back-up harness and plan on putting it in tomorrow.

 

[Josecuda]

Having the exact same problem with my duster. With electric load alternator shows 18v. While the battary says 14v. Great help I've found here, now I know where to start searching for the culprit of my electrical issue.

 

[Sinister.]

I pulled the bulkhead connectors off today and found a rather nasty surprise... nearly half of the alternator wire contact was solid white from corrosion. I cleaned up all of the other contacts and pulled the alternator wire from my back-up harness and plan on putting it in tomorrow.

changed my mind on this idea. I'm going to go from the harness, through the firewall, to the alternator with some new 10 gauge. Hopefully tomorrow. I miss my car

 

[Sinister.]

well the work is done... for now. I ended up replacing about 3/4 of my engine compartment wiring harness because I was already there and I had a spare harness. After everything... SHE RUNS GREAT! whoo! Even loaded with everything I can put on it, in drive, it doesn't even think about dieing. I'm in the middle of body work but I don't care, I'm bolting headlights down and throwing turn signals in tomorrow so I can drive her for a day.

Thanks everybody!