I am installing a Pertronix in my '73 F100. First thing I did was check the voltage at coil with key in 'run' position & engine off and it reported 12.5 volts (battery was 12.6).

Since there was no voltage drop, am I correct in thinking this truck does not have a resistor (or, resistor wire) to the coil? Everything else is stock, so the only conclusion I can come to is the coils have internal resistors? Used to GM products

 

You have to be careful when taking this measurements with points. The points must be CLOSED for this measurement. If the points happen to have landed OPEN (which can happen, at reduced probability), the coil will read 12 volts regardless of the presence or absence of the ballast resistor. The truck would have had one from the factory, so please verify your measurement.

 

Is it a physical resistor or wire I'm looking for? Assumes a faulty initial reading

 

To be clear, the intent of my last post is to tell you that if you are trying to "smoke out" the resistor using a voltage measurement (which is the proper procedure), you need to verify the position of the points to qualify your voltage measurement.

That means, if the meter reads 12 volts, pull the distributor cap off and verify the position of the points. If they are open, bump the engine over until the points fall off the high step of the cam so that they may close, then repeat the measurement.

To answer your question directly, the factory ballast resistor is a long length of wire. It's made as a long wire instead of a single piece so that it may better dissipate heat. It's typically bundled in the harness and not always easy to spot. Or, sometimes it's there, but someone has bypassed it. That's why the proper way to check for it is to measure it, like you're doing; you simply must ensure the points are CLOSED.

 

Thx, I immediately suspected my measurement was at fault, rarely lucky enough to hit the easy install upfront ...will place an aluminum conductor between points to ensure they are closed

 

I don't recommend placing extra material down in the distributor. If they're open, just bump the engine over to let them close. No need to over-complicate.

 

Thanks for the info; bridging the points (fragged, wouldn't run) still 12 at coil. 20 mins later, all better w Pertronix. Looks like someone craftily ran a wire alongside the resistor wire to look original. They also installed a internal resistor coil based on the ohm reading, so for once, an easier install. Get lucky only only once in a blue moon, guess I should plan on harder way around for awhile...thx - PM

 

Makes sense to me. Glad to hear you got it worked out. Pertronix is good stuff; I've got one in my '71 LTD. Enjoy!