On my 71 1-ton when I turn the key to the on position I have no power; no lights, no radio, no heater fan (it won't crank either in the start position). I traced a heavy gauge red wire from the battery back to the firewall and I have 12 volts there, but I am wondering where to go from here to trace the problem now such as ignition switch, fuse panel, voltage regulator (external), fusible links or some ground problem. It is fine when cold and you let it sit overnight, but there is some problem that is getting hot and building up resistance to prevent it from getting power and being able to start.

I am about ready to just rip out all the old wiring and start over as there are lots of wire splices for a dual battery setup, winch, trailer brakes and lights, etc.

Thanks for your help.

Unplug the ignition switch and look at the plug. I'm betting a kick in the gut the problem will be painfully obviouse at this point.

is the battery got a charge?

Longhorn: I have tried replacing the ignition switch with another one before and that doesn't help, but I will check again. Do you mean that the plug and wire harness is bad, and is the switch grounded to the back of the dash?

hvychve: The battery is fine. It is a new Optima 880CCA battery; the cranking voltage is 10.8.

I believe it may be the main power feed wire that I mentioned before. I just noticed from the wiring diagram and another truck I have here that it is directly spliced into the front harness. There is no small junction block on the passenger inner fender or fusible link. Could that be the problem even though I get 12V on the drivers side firewall junction block?

I figured it out (for now). The PO had spliced an aftermarket ammeter gauge directly into the main power feed line in series, even though the factory in dash gauge works fine.

My concern now is if I put it back right that something else won't burn out, as I mentioned above there is no longer a fusible link in the line...

Add a fuseable link back into the line. If there was one there to begin with, you do not want to do without one or you will be asking for trouble. Did the ammeter burn out also? If it did, spend a little extra time going through all of the wires. And make sure you have the vehicle parked outside until you are totally satisfied that the wiring is in A-1 shape. One of the biggest causes of vehicle fires is faulty wiring. No use taking the house with it.

Kevin