bought a 74 f 100 4x4 390. This truck is still not quite roadworthy so still don't know all the bugs that need working out. Any way about 3 months ago I was running the truck and it kept shutting down(no spark) then it would fire up a while later. So I figured I would get rid of the old box module or whatever its called. I put a used 6al box, msd pro billet dist, and msd coil. Well it started right up and i drove it around the block a few times, ran great. and would always start up fine since. I couldn't even get it around the block with the old setup. any way today I start it up and back it out of the shop, go to get in and start it up, doesn't start?? No spark. put another coil in it still nothing. my buddy hit the starter solenoid a few times and when he was holding the plug wire to the block we got spark for a second, but nothing since. Could this be a solenoid, or a ignition switch. How do I test these items to see if their toast?? Thanx in advance

 

I would hot wire the ignition temp to the battery. If it starts, then you know your components are good, and there is a wiring problem with the truck.

If you find it is a wiring problem in the truck, it may be hard to find if it's intermittent. If it's dead, and stays that way, you can take a meter or testlight and see if you have voltage coming out of the ignition switch. If it's a intermittent problem, you could wire a light to the ignition switch and when it quits, you can quickly look down and see if the light is burning to indicate you have voltage there.

The ignition switch is fed voltage from a wire usually connected over at the starter solenoid, and there are usually splices in this wire feeding the fuse box and the alternator, so you might have to slowly trace the problem all the way back to the solenoid. Remember the solenoid has nothing to do with the truck running, only with the cranking of the engine, but where the bat + connects to the solenoid is usually the same spot where they tap off for power to run the rest of the truck's electrics.

 

i have a 74 390 with points, i put the engine in a 51 ford, it has new points condenser, cap rotor and new distributor, i still have no spark at the plugs, i do have voltage to the points, im stumped! please help

 

Put your + meter lead or testlight to the negative terminal of the coil(the terminal that goes to the points).
Put your - meter lead or testlight lead to a good ground on the engine.

Crank the engine over. The meter should move up and down or the testlight should blink while the engine is turning. If not, your points are not making contact, or your ground wire inside the dist is bad.

The coil gets a constant hot on it's + terminal with the key in run. The points ground and unground the - of the coil and that's what makes the spark.