ok i put a new wireing harness in my girlfriends truck a 55 f-100 with a 351-m .the problem i am having is if i turn off the switch the motor keeps running until i pull out the fuse going to the coil..i checked the switch with a test light .in the off position the motor will still stay running but test light shows no power going to coil..today i ran a new wire from the coil to switch. same thing motor keeps running had to disconnect wire at coil to stop it ....can any one help me out on this ....
Sure. You have another wire sending power to the coil that isn't supposed to. Once you find that mis-wired wire, you'll be all set. Only you know what you've done, so only you can find it. It could be anywhere along the ignition circuit.
Wiring problems are among the most frustrating issues in the automotive industry. But once you find them, they're always something simple. Good luck with your search.
Welcome to the forum. What type wiring harness are you using that has a fuse in the coil circuit?
1949 F-4 Built to drive--script bed.
1956 F350 Stock rebuilt script bed
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the wiring harness is a painless wiring harness #10202 i bought it off of one of them auction sites on the net the guy had bought it but never used it ..i liked it very simple stright foward follow directions ..i have to pick my days that i can work on mine an her trucks cpl hours at a time taking a lot of heavy pain meds ..dav...i wired my 56 with an orignal type harness it worked out great...only had to fix bout 2 bugs after i finnish with it ....
I think you should re-check the wire that you have going to the coil. Painless labels every wire with laser printing along the way. I have a painless harness....I don't have it fully installed yet, so I'd have to look to see if there's a fuse in the coil circuit. It sounds like you have some other wire attached to your coil.
I had this problem on one build, ended up taking it to an auto elec who put a diode on the alternator wire. I never did understand fully but the alt somehow kept energising the coil circuit and the switch did nothing, he said it's a common problem on looms that were meant to run generators and regs but are now running alternators. The car had been rewired although not with a painless harness.
FWIW, I installed a new harness in my 48 F68 (F-3), and couldn't get enough power to my coil to run the engine, after changing a lot of parts I finally traced the problem down to the yellow wire under the dash that was suppose to run power to the coil from the ignition switch ran out of the harness as the fuel sender wire and vice versa-(both were color coded yellow)- ie my fuel sender wire was the coil wire and the coil wire was going to my fuel guage. So after running through the fuel guage the wire to the coil had 6V, but no amps to make things work, what a PITA, but I got them swapped and everthing works great now. Moral of the story, cant always count on new parts to be correct and double check everything.
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48 F-68 Nut and bolt restoration/mods-power brakes, 16.5" 8 bolt wheels, reds headers, signal lights and seat belts.
This is a common problem with MSD ignition and Ford alternators with external voltage regulators and maybe some other arrangements. There is feedback through the charge indicator light to the ignition circuit. Installing a diode in the circuit will remedy it.
I had the same issue on a Jeep w/ GM Alt & Painless Harness and as said above it ended up being feedback from the alternator. It has been several years but I believe the instructions or web site may have had information on this.
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