Hey guys. I have a 1965 F100 LWB, 352, 3 on tree, nine-inch sporting 3.50-1.
My question regards this ignition resistor wire that I have heard of. When I bought my 65 earlier this year I noticed a ballast resistor wired into the ignition circuit.
I thought it odd, having only seen them on Dodges but shrugged it off as may be necessary for the Mallory pointless distributor with 12v coil.
Well, it has been giving me issues. I need to know is the ballast resistor needed? What should the voltage to the coil be through the resistor wire, if it is there,
and if it is not can't I just get a coil with an internal resistor to get rid of the darn Chrysler parts and clean up the engine bay.
Also, if I must keep it, is the intake manifold too hot of a place for it? I moved it there from the fender for appearances.

 

Old points system need the resistor. Ford Duraspark II systems need the resistor. Ford TFI systems do not. GM HEI systems do not. Most of the newer Pertronix systems do not. You will have to check with the manufacturer of the ignition system you have, to see if it's required. If it is, you will need it to keep from burning out your ignition system.

The resistor is like a cushion of sorts. It feeds the + of the coil. The circuit then goes through the coil, out the negative of the coil to the points, or the electronic control box, whichever you have. The points or the electronic control box grounds the negative of the coil, and then when it ungrounds the coil the coil fires a high voltage spike out of the center, the rotor in the dist points it to the correct sparkplug, it travels to the sparkplug and lights the air/fuel mixture.

I will repeat this, the coil generates the spark when the ground is lifted on the negative of the coil by the points or the electronics. When the ground is then re-applied to the coil, the + wire to the coil "fills up" the coil with 12v.power. When the ground is lifted, this stored energy "jumps" to the many windings of the secondary of the coil, and that is what generates the high voltage spark.

I will finally get to what the resistor is for. When the negative of the coil is grounded, there is a initial spike in current which is very high on the + power wire to the coil. As the coil fills up this current is less and less. To control this initial spike and "soften the blow" to the points or the electronics, a resistance is used. Ford used a special wire on a lot of their cars, but they did use the large white resistor also. I believe Gm also used a wire sometimes, Chrysler seemed to stick with the resistor. The resistance is not very much, usually around 1 to 1.5 ohms. But you can see it's pretty large, and it does get hot. Don't let any wiring or plastic touch it, it may melt it. It should be ok on the manifold as long as it has some room around it to shed heat.

With the Ford TFI and the GM HEI, they have circuitry built in to regulate the current through the coil. Like I said you need to find out from whoever makes your ignition you are using, if you need a resistor or not.

 

I appreciate your very concise tutorial on how the ignition system works.
But my question remains, how do I know if the resistor wire to my ignition is intact? What voltage should I expect to see on the b+ coil wire if it is there? Before the ballast resistor.

 

volt meter to before side of the resister you should see about 8 volts if the wire is still there. if not you will see 12 volts.

 

Perfect. Thanks. What do you know about the older Mallory distributor, electronic not points, no box just dizzy and coil, can it take battery voltage?

 

they say they can, but i never had any luck putting 12 volts to it. had 2 burn out within a year. after dropping voltage the next one is still running fine 30 years later.
even with the pertronix units in all my old cars and trucks, i limit voltage to around 8 volts. they just run happier and last forever.

 

I got out a dvom last night and found 11.4 volts at the B+ wire going to the ballast resistor. Battery voltage was 12.6 so I know my meter was working right. Coming out of the ballast I read 10.5. not sure what to make of these findings.

 

What if I run a coil with an internal resistor? I was told to use one on an old Flathead that I was converting to 12v neg ground. Seems to be fine so far but no real miles on it.

 

The engine must be running to take the voltage readings. No current flow, no voltage drop.

 

Just to wrap this up for future readers, the original resistor wire was intact as verified by voltage reading at idle. I removed the ballast resistor, soldered and shrink wrapped the wires together, ensured a good ground, and replaced the terminal ends of the wires to the coil that had questionable crimps and the truck is running great without a despicable looking piece of Chrysler hardware uglifying up my intake.