Ballast Resistor

Q: Ballast Resistor

Does anybody know what the voltage going in and out of the ballast resister should be? I know I asked before but is a resistor wire going into the ballast resistor normal? Also our new resistor seems to get quite warm…is this normal when new? or always? The wiring going in and out seems fine. Also is anybody using an Accel supercoil? You know the big kinda boxy yellow one…does it have internal resistance? If so does that alter the requirement for an external ballast resistor or resistor wire?

Here are my particulars…My Accel Supercoil has 1 ohm resistance so I’m assuming it has no internal resistance. With my ballast resistor in place and connected i have like 9.6 volts going in and only like 4.6 going out to the coil. But if I disconnect the ballast resistor I have 12.3 volts coming from the resistor wire. If I connect the resistor wire (coming from the ignition switch) to the ballast resistor but dont connect the wire from the ballast resister to the coil + I have 12.3 volts at BOTH sides of the ballast resistor. Then when I hook the wire from the resistor to the coil my voltage drops back to like 9.6 going in to the resistor and 4.6 coming out and the resistor gets quite hot. The ballast resistor itself has 1 ohm resistance across the terminals with nothing connected. Also the ballast resistor gets so hot that it actually smokes but the wiring seems fine on both ends

A: You should NOT have BOTH a resistance wire AND a ballast resistor. I think our Firebirds (at least in 1969) used a resistance wire. If you have a coil with internal resistance, then you should NOT use an external resistor or resistance wire. If you want to know if you coil has an internal ballast resistor, measure the resistance across the coil. It should be 1.0-1.5 ohms if there is NOT an internal ballast resistance and about 4 ohms if there is.

Information about your configuration (ballast wire/resistor/internal coil) and what the voltages should be at different places:

First, you will always get battery voltage (12.3 in your case) at the end of the wire going to the coil when it is NOT connected. You could put a 1k resistor on the end and you’d still get battery voltage. This is because currect is not flowing and the Potential of 12.3 Volts is still there.

Next, I’m assuming that when you took your voltage reading that you grounded the “-” side of the coil or made sure that the points were in contact, with the ignition in the “on” position but the car not running. If so, then your reading indicate that your resistor wire is about 0.6 ohms. That is just about what it should be. That being the case, I’m not sure why you have a separate ballast resistor at all. Does it look factory, like it aught to be there? If not, ditch it. Your 0.6 ohm resistor wire and 1 ohm coil will give you about 7.5 Volts to the coil (static) which is fine.

As a side note, during cranking you should have full battery voltage to the coil to provide a “hotter” spark. This is accomplished either by a wire to the coil from the starter OR a separate wire from the ignition switch “start” terminal.

DON’T STOP READING.

Having said everything above, I just read the ACCEL catalog. It says:

“NOTE: ACCEL 140001 Super Coils are supplied with a 0.85 ohm Ballast Resistor which must be used in conjunction with the vehicles original ballast resistor, if equipped”

I think I remember you said you had a super coil. If you do and you’re using their ballast resistor, I’d call ACCEL and find out why it gets so hot and smokes. That or go back to a standard coil.

A: GM didn’t use ballast resistors, they used resistance wire to the coil. The voltage at the coil should be about 9 volts. The yellow accel supercoils used an extra ballast resistor to lower that to 6 volts. Sounds like someone did a little creative wiring. Maybe they replaced the resistance wire to install a GM HEI distributor, then changed their mind and rather than find resistance wire, used a ballast resistor, plus the one for the super coil.

Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.