C3 Coil resistance wire, proper voltages?

[Scott Marshall]

Hello, can anyone with a 72 vette tell me what voltages they read on the resistance wire (hooks to the + side of the coil) with the ignition in the OFF, ON and START positions. The problem I have is that I burned up my distributor the other day. Since then I have been going over wiring diagrams and reading manuals like crazy. It is MY understanding that in the OFF position voltage should be 0 volts, ON position 7-8 volts, START position 12 volts. What I have found on my car is the OFF position 5.5 volts, ON position 12 volts, START position 12 volts. This is with the wire disconnected from the coil and the yellow wire disconnected from the starter solenoid. The engine wiring harness is new. There seems to be 5.5 volts coming from somewhere else. Is this normal?
Please help!
Thanks
Scott

[William C.]

Re: C3 Coil resistance wire, proper voltages?

key off voltage should be zero between the wire terminal and ground or the coil terminal and ground. The yellow wire is only operative during cranking, as it is activated by the pull-in of the starter solenoid. What do you mean "burned up" the distributor? This is not a common event.

[Scott Marshall]

C3 Coil resistance wire, proper voltages?

I have a Mallory Unilite distributor installed on the car. It ran great for the first couple days and then it started misfiring and then it wouldn't even start. I started checking voltages on the ignition system and found the results I posted earlier. Mallory stresses that during the installation of the distributor that you must use either the loom resistance wire or a ballast resistor to drop the voltage to 7-8 volts. 12 volts for longer than the starting cycle will damage the module. It seems like the resistance wire has somehow lost its resistance or the extra 5.5 volts on the circuit initially plus the normal operating voltage on the resistance wire has bumped it up to 12 volts.
Thanks
Scott

[William C.]

Re: C3 Coil resistance wire, proper voltages?

The chances of the resistance wire changing it's voltage is somewhere between slim and none. The problem is that the resistance of this wire is very hard to impute from a voltage measurement such as you are doing. Unless you can actually maesure the resistance with a very sensitive ohmmeter, I would suggest that you just look for another source of your problem. If you want to be safe, just wire in a straight 12v curcuit and use a ballast resistor if you feel you have a short somewhere.

[John H.]

Re: C3 Coil resistance wire, proper voltages?

I've used Mallory Unilite distributors on several project cars in the past, and Mallory sells a ballast resistor for just that purpose. If you're seeing any voltage in that wire with key "off", you have other problems that need to be run down from the ignition switch through the bulkhead connector.