So, I've owned this truck for a while and have been removing the years of add on wiring as I do stuff to it. Well I just rebuilt the motor and in doing so removed some wiring ie extra oil sensor wire and spliced in thermostat gauge. I guess when I was doing this I cut out a ignition power wire off of the resistor on the firewall. Found that out with no spark. So here is my problem. I rewired it and only get about 11.5V to the first side where I remade the connection. I have done nothing else to the electrical system. The other side where the wire runs to the coil is only sending out 3.5V to the coil when the ignition is on. Now, I'm not good at this stuff so............It came to me with a mallory aftermarket coil part# 28720 and it looks like they changed out the innards of the distributor with mallory espark or something like that. This truck was running fine before lol, I don't know what I did, however it should be simple to figure out and I can't. I can't find info that says how many volts the coil should be getting. Also, i did initially hook a wire to it off the "BUS" that was constant hot and it was shooting lightning off the coil post to the firewall...thats how I figured out it wasn't powered from the ignition. Anyway,...is it possible that the resistor took a dump? or did I fry the coil? It will produce spark when i crank it over from the post to the firewall, but i think it should be more. I can't find any info that says what the coil is supposed to be getting other than ohms.

Thanks in advance.

VIN says it came with a 360 people i bought it from said its a 390 and most of the old paperwork references 390.
1973 F250 ranger 4x4

 

If the internals of your distributor were replaced/upgraded, it is most likely, they run of true 12v current. Most modernized distributors and retrofit modules like Pertronix, Mallory, etc... tend to need the higher voltage, w/o a regulator. Without knowing exactly is in your distributor, it'd be hard for me to say that's definitely the cause.

 

Take your distributor cap off and post a picture of the internals, it could be an old points and condensor, a duraspark, or some aftermarket job. At least then someone can point you to a suitable coil or how to power it. The originals run the positive terminal of the coil from the resistance wire to drop the voltage for the old points distributors, this may be way your seeing a low voltage since the lower coil resistance is causing more current to be drawn and hence more drop across the resistance wire.