Ballast Resistors

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Bullypit

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During the past week the Mark II I am bringing back from the dead has experience hard starting when hot. Since I have been working on it, I have replaced the points with a Unilite (inside an older Mallory dual point), I have put on a new Mallory coil, and a new set of MSD wires. I have not changed the ballast resistor, and it may well be original to the car.

Yesterday I almost got stuck at a restaurant, and had some friends with me to help diagnose. The carb is getting gas fine, but it appeared that it was not getting spark. While another cranked, I momentarily bypassed the resistor and it fired right up. I immediately reconnected to the resistor and the car ran OK as I took it home.

I suspect the resistor is opening up when it gets hot. I know SS has replacements, but I have a couple that I have not used in the past laying around. Does anyone know how many ohms the resistor should be, and what the voltages should be before and after the resistor when the car is running?

Also, is there a particular replacement I can run to the NAPA/Pep Boys and purchase as a quick replacement?

Any input would be appreciated.
 
Bullypit said:
While another cranked, I momentarily bypassed the resistor and it fired right up. I immediately reconnected to the resistor and the car ran OK as I took it home.


Any input would be appreciated.
Click to expand...


That's curious as when the key is turned to the 'start' position, a wire ( white with blue stripe? )that runs from the solenoid to the coil side of the ballast resistor should be 'hot' and supply 12 volts while the engine turns over...when the key is released to the 'run' position, this wire is 'off' and the voltage has to go through the ballast supplying probably 8-9 volts...

If that wire was hooked up, you would already have 12 volt going to the coil ( bypassing the ballast ) and what you did would make no difference so that tells me there may be an issue with that wire


Jim
B382000446
 
I just tried testing a fairly new, no longer used resistor but it was shorted. I dug out my shop manual and it says (section B, page 65) the ignition coil supply is 6-7 volts. (6-7 or 8-9, what's the difference of a volt or two between friends:)).

More importantly, the manual says that there is an additional contact in the starter solenoid that shorts out the ballast resistor during starting mode. That is essentially what you did manually to get the car started. So, in addition to there possibly being a wire problem, there could be a starter solenoid problem.

Gene
 
...from the wiring diagram, I've highlighted ( in red ) the circuit that should go hot ( 12v ) when the key is in the 'start' position bypassing the ballast resistor. If you test the coil side of the resistor with the key 'on' and then turn it to start, you should see the voltage change ( rise ) at that point... if not, it's either the wire or the solenoid...

Jim
B382000446
 
BALLAST RESISTORS

I am not familiar with the MALLORY unilite unit but my PERTRONIX ignightor eliminates the ballast resistor, and runs on full 12 volts. The ballast resistor lowers the voltage to the points to 6 volts so you don't burn the points as quick. Eliminate the points and you can toss the ballast resistor.
 
I have a Pertronics distributor and Flamethrower II coil on my Tiger and it's meant to run on 12 volts without the ballast resistor...
I had a Mallory Unilite back in the 80's and I'm pretty sure I still ran a ballast resistor with it but I have no idea if a 'newer' one still requires it...


Jim
B382000446
 
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