Sampson

Went to the parts store to purchase a new coil for my car. All of the numbers called for an external resistor coil. My old coil has been painted and I cannot tell for sure which it is. It has been a year since I tore the car down but did not document an external resistor anywhere. Most ballast resistors I am familiar with (Mopar) are ceramic and mounted on the firewall. I suspect that I need an internal resistance coil. The only other possibility is the small condenser looking resistor attached to the - neg side of the coil. Looks more like a radio suppressor similar to the one on the voltage reg. Can anyone steer me in the right direction?

jensenracing77

What year? You likely have a pink resistor wire going to the coil. The resistance is built into the wire. I like it this way better than the ceramic but if the wire has bad spots and is cut shorter with a new regular wire spliced onto it the resistance value will change.

m371961

I believe Ford and GM had resistor wires, Chrysler had the firewall mounted ceramic resistor. You can disconnect the wire at the coil from the ignition and check volts to know for sure what is there. The condensor is for the radio.

joe_padavano

Do not confuse an internal resistor coil with a resistance wire built into the harness. The resistance wire, which is what GM used on a point-style distributors, is still an EXTERNAL resistor, meaning that it is not built into the coil. The fact that it is built into the wire in the harness instead of a separate ceramic resistor is irrelevant, they still function the same. Internal resistor coils have this resistor built right into the coil. That is NOT what GM used. This is one time when the auto parts stores are correct (hey, it happens occasionally). You need an external resistor coil. The resistor is simply built into the harness.

Sampson

Thanks for the education guys. You are right (as usual) I checked for resistance in the wire and it is there. I was just concerned that I could not find the external resistor. This is a newly rebuilt engine and I want to make sure that everything is right on the first crank. Hope to fire this baby up this weekend!

Octania

The cars built before HEI have the resistance wire.
It is not pink, that's the HEI's larger ordinary Cu wire.
The resistor wire as I recall has a checkered pattern, maybe looks braided. Does not look like an other wire on the car.


Don't you have to have current flowing thru that wire in order to attain a voltage drop across its resistance? I am pretty sure that with no current flowing- the wire off the coil and connected only to your voltmeter- the voltage present at the coil end of the wire will be pretty much identical to that at the battery. A voltmeter, ideally, allows no current to flow during measurements.

MDchanic

Octania is correct on both counts:

The insulation on the resistor wire is a braided sort of affair, as the wire can get hot (resistance that varies according to temperature is an inherent feature that helps to regulate current flow into the ignition system), and you wouldn't want to risk melting the rubber.

In order to accurately assess the presence of a resistor wire using a voltmeter, you need to have a load on the wire (the coil is good), or the voltage you read will just be battery voltage (13v). Remember that while the points are open, the coil is not in the circuit, so the voltage will read "high" until you rotate the engine or the distributor enough to close the points and connect the coil.

- Eric

jensenracing77

lol, Brain fart.... We use a resistance wire at work and it is pink. It is used to build heat in the drain lines to keep them from freezing. They are always refered to as "pink resistance wire". The ones on our cars are a pink and black braided wire like they said above.