46 P/U electrical issues

[Deleted User]

My truck is blowing head/parking light fuses like a champ.

Is there anywhere that I can get a wiring diagram or is there a common cause (besides 60 year old wires) like the switch going bad?



It blows the fuse immediately when the light switch is clicked on.

Jon B

You might want to state which year pickup you have (in case someone has a diagram handy and can e-mail it).



The cause would probably be a short. Somewhere, that old cloth-covering on the wires has frayed, and the bare wire is touching something it oughtn't touch. Inspect carefully (better yet, gradually replace your wiring with modern wire bought at your local parts house!). Often, the wiring harness passes through the firewall and the rubber grommet has worn away. This the insulation wears away on the sharp edge of the sheet metal and...voila! Another short!



There might be a problem with the switch but I think it's not as likely as a short in the wires. To be sure, remove the switch and put a continuity tester on it to see if there is a circuit from any of the terminals to the switch body.



And...get on your back and shine a flashlight up under the dash. Do any of the wires (from the switch) rub agains the cowl vent lever, or anything else down there?



Check around the dimmer switch too (while lying under the car) to see if the wires there are shorting.



Of course, the problem could be a short back by the taillights as well, or at the parking lights! Try isolating the problem: disconnect all wires from the headlight switch, then re-connect them one by one until you blow a fuse. That will at least tell you which circuit the problem lies in.

Unknown

It's also not uncommon for the cloth to fray within the Parking Lamps, Tail Lamps and Headlamps. A good disassembly is probably in order to make sure that the cloth isn't worn through at the socket itself.

[Deleted User]

I've already replaced all the wires going to the lights, I am guessing the problem is under the dash somewhere.

[Deleted User]

Ok, The fact that the fuse does not blow until you turn on the lights means that the problem is somewhere between the switch and the lights. My guess would be that you will find a chafed wire under the dash.

BJ--TN

Uncle Josh

There is a 2-page electrical diagram in the 41-47 mechanical procedures manual, available from the HET store.

[Deleted User]

I found the short...It was where the harness runs through the firewall, some insulation on several wires was worn through.