Hello all fist off thanks for looking reading and helping this site has helped me so much over the years keep my truck going and I cant thank you all enough. So here's what's going on 1973 f250 custom 2wd hasn't been daily driven for 2 or 3 years due to navy and long term motor swap. (Got the motor in broke in and then got water in the oil riped it apart and found a host of problems it's now a 445 fresh rebuild. On the first start up discovered no spark. I used to have a msd 6al box and new ready to run distributor. Took the box off for this build to just keep it simple. So I'm just using the ready to run distributor. Have 12v at the coil + drops to 6 when cranking. But I'm not getting much spark I'm using a timing light to check for spark directly off the coil I get a few pulses in the first few seconds of cranking then nothing. Same when using a spark plug directly off the coil checked engine grounds ran a 12v jumper off the battery. It was a bit better but still orange spark and only a few then nothing. Checked oms on the coil was fine but tried a new one anyways still same thing. Tried changing the battery out still same thing. I'm completely confused. Anyone have any ideas? Unfortunately my usual rule of thumb (the last thing I touched I screwed up) don't help much because I've redone almost everything in the engine bay. Thanks for reading.!

 

One thing before we go to far: Does the distributor rotate when you crank it? Take off the distributor cap, crank over the engine, make sure the rotor is turning.

I'm not entirely sure anymore, but at some point, the starting system included a way to jack up the voltage to the coil while starting. The ballast resistor usually keeps the coil voltage around 6V or so when running. When starting, that ballast resistor is bypassed so that the voltage goes to full 12V when cranking.

It sounds as if whatever circuit supplies that start voltage is cutting out or not energizing at all, as you turn the key from "run" to "start". It very well could be the ignition switch. Some systems also had a tap off the starter solenoid on the passenger-side fenderwell, that when the starter solenoid was energized, it would supply voltage back to the coil.

Also, I once burned out an MSD 6AL by disconnecting the coil wire from the distributor and not letting it arc to ground. So whatever you're playing with, always make sure the energy in the coil has somewhere to go.

 

So just to understand it better- fresh build, same MSD and distributor as old engine but got no spark. Pulled the MSD out of the equation and ran the same coil as before. Essentially the coil was getting power from the box and not the stock ignition wiring. Taking the box out adds in the resistor wire off the ignition switch unless it's been cut out already.

 

Art is correct, there are two sources of power to the coil. One source provides full power in the "start" position, the other goes through a resistor, or resistor wire, and supplies reduced voltage to the coil. Sounds like you somehow have it backwards. Verify voltage in both the "run" position (reduced voltage) and the "start" position (full voltage). This usually requires two people to accomplish. I cannot get into the specifics of the actual wiring because I've seen Ford do this in various ways. Typically they use the switched side on the starting solenoid ("I" post) for the start power. This assumes that the solenoid is wired correctly.

It ain't evil if understood.

 

Thank you everyone for the help I'll give that a shot once I'm back from this underway

 

If you use a Pertronix system you can just feed 12 volts all the time and not worry about the ballast resistor. Also no more points.