question about coil/wiring

[Tooltime76]

Hello,


I am wondering about the Coil/wiring in my 68 Fury, when ignition is on (without enginge running), the Coil measure from + to - connector just 3 volt. I guess this is a bit low, right? It also takes quite some time to get the engine running, could this maybe be the issue?


On the + connector of the coil there are 2 wires, one is going to one of the FLD connectors on the alternator and the other on is going to the ballast resistor.
The prev. owner replaced the old alternator with one that has 2 FLD connectors. But the voltage limiter was still a "old" mechanical one, I replaced it with a plug and play solid state one (Regitar C524). So I guess the second FLD connector should be grounded instead?

On the ballast resistor on one side I measure 12 volt and on the other 3.2. Could the ballast resistor be faulty?

When everything is ok I should end up with approx 8 to 9 volt on the coil, or?

I have a point distributor and the coil needs a external resistor.

Best Regards
Stefan

 

[Wildaugust]

Yes, the voltage at the Positive (+) terminal of the coil should be around 8 volts and should not be less than 6 volts. The Ballast Resistor could be faulty if it only has 3 volts at the coil side when there's 12 volts going into it.

The later style dual field alternator can have either one of the FLD terminals grounded if you're using the old style Voltage Regulator, but I'm not familiar with the regulator you mentioned. Someone else will chime in on this one.

 

[Wildaugust]

OK, I just looked up the VR and it looks like it would be wired in same as the old mechanical VR. So, one alternator FLD terminal would be grounded.

 

[Tooltime76]

Thank you very much for the answer. Will ground the fld terminal and get a new resistor.

 

[Wildaugust]

Thank you very much for the answer. Will ground the fld terminal and get a new resistor.

Your welcome. I should've mentioned too that you could check the Ballast Resistor before removing it. The Ballast Resistor should have a resistance of somewhere between .5 to .6 Ohms, or at least be very close to that. The reading shouldn't change even if you carefully jiggle the terminals of the resistor while the test leads are hooked up.

I hope this helps.

 

[BillGrissom]

You can't judge by measuring coil+ with the engine not running. If you still have a points distributor, you would measure 12 V if the points happened to be open and 3 V might be reasonable if the points are closed. BTW, I read you can damage the points (or even the later electronic box) if you leave the key in "run" with the engine off for too long. When the engine is running, the points are opening and closing and your multimeter reads the average coil+, which should then be ~8 V. The capacitor there (for radio) also smooths the voltage.

Check your wiring diagram, but I don't think an alternator field should come off coil+, but rather from IGN1 (upstream of ballast resistor). Anyway, that is for a 2-wire alternator, which a P.O. kludged in. You are correct that you should ground one brush and connect the other brush to the Vreg "FLD" terminal. Doesn't matter which brush is which.

For those wanting to upgrade to electronic spark control, there is an inexpensive distributor (~$60) on ebay w/ integral HEI module. You can then eliminate the ballast and all its confusion and weaker spark. You can also install a later Mopar e-distributor to trigger a GM 8-pin HEI module (from 85-95 V-8 truck, also grab knock sensor/module). That is my plan, but only so my engine controller (Holley Commander 950) can control the spark.