1977 Ford F250 400m electrical problems

It doesn't sound like a ground, but there does exist an engine to body ground strap the gets forgotten quite often. It is located at the rear of the engiine going from an intake manifold bolt tothe firewall. Check the charging voltage of the alternator at the battery posts. The charging rate should be between 13.6 to 14.2v. Remember this, The higher the voltage the lower the amps In turn the lower the voltage the higher the amps. If the alternator is charging at 14v, it should drop towards 13,even as low as 12v, depending on the battery and accessory loads.At 12v, the alt is pouring out some serious amps and running hard. This is not good for the alternator. That's the reason for 13.6 being nominal. If the alt puts out 15v, this is also harmful. Although you aren't getting the amps, the high voltage will burn up things designed to run on 12v, Like lights and radios, relays and such. I hope all this makes sense to you and is of help. Check the eng to firewall grd, Ck your charging voltage and give your battery ground a second once over at both of the cable ends, loosening the bolt on the engine end and making sure its clean. Checking the + connection wouldn't hurt. Good Luck, Ned. Let me know, k?

There should be a ground strap from the engine block to the trucks frame, if there isn't one you must install one. The coil can make as much voltage as it wants, but if it cant find its way to ground after is goes through the plugs then the plugs are not going to fire well.