75 F250 lighting wiring problem - Help
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From: Lincoln University, PA
75 F250 lighting wiring problem - Help
I have a 1975 F250 XLT Ranger Highboy. I have a problem on the brown circuit 285 wire which according to the wiring schematics in the Haynes repair manual should be carrying 12 volts to the lights when the headlight switch is turned on. I get 12 volts when the headlight switch is turned on alright, but the same circuit tests as ground when the headlight switch is off. This doesn't seem normal to me. I expected to see no reading with the headlight switch off. Am I correct or is the wire supposed to be grounded when the headlight switch is off? If not, can someone suggest a course of action to correct the problem? Thanks.
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From: Lincoln University, PA
I had the opportunity to check the same circuit on a friend of mine's 1979 F150. I was surprised to find that the brown wire circuit 285 on his truck also tests as ground when the headlight switch is off and positive 12 volts when the headlight switch is on. So unless both trucks circuitry is wrong I think I have no problem. Can anyone add anything to this. I have never seen a circuit designed that way.
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From: Lincoln University, PA
I had a wiring spaghetti jungle between the grille and the radiator support from the addition of the years of a snow plow, snow plow lights, fog lights, high intensity off road lights and a switch over from sealed beam headlights to halogen style round headlights. Over the course of the prior installations I had to control the off road lights with a relay and the halogen lights with 2 relays (one for high beam and the other for low beam) because they drew too much amperage for the high beam / low beam floor switch and the headlight switch. Both burned out previously. Anyway I was having headlight and turn signal problems this fall and finally decided to clean up the mess. So I began cutting out all the wiring and starting over checking each circuit as I went. I was surprised by the ground when off / 12 volts when on situation so I figured I had an erroneous ground problem on that circuit. But before I spent hours tracing out the entire circuit I remembered that my friend had a similar truck (79 F150 vs my 75 F250) with the same circuitry according to the wiring schematic. Anyway as long as it apparently is correct as wired, I can now complete my rewiring job.
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[QUOTE=StevePimer;8087183]I have a 1975 F250 XLT Ranger Highboy. I have a problem on the brown circuit 285 wire which according to the wiring schematics in the Haynes repair manual should be carrying 12 volts to the lights when the headlight switch is turned on. I get 12 volts when the headlight switch is turned on alright, but the same circuit tests as ground when the headlight switch is off.
Steve
Was the connector to the headlight still connected when you read the ground in the circuit? If so, you were reading through the headlight filament to ground.
Steve
Was the connector to the headlight still connected when you read the ground in the circuit? If so, you were reading through the headlight filament to ground.
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