I've recently replaced both headlamps in my 1980 F-100. It's causing problems by illuminating the left turn & hi-beam dashboard bulbs. But before I start tearing into things, I'd like to at least verify the order of the wiring in the headlamp connectors.

What the Haynes' manual shows is this: as you face the truck, the left headlight shows (from left to right) grn/blk, red/blk, and black.

The right headlight shows the same thing; from left to right it's grn/blk, red/blk, and black.

I thought this a bit odd; I've read elsewhere on other websites that the center prong is the ground, but according to the wiring diagram in the Haynes manual it's the right-most prong (black).

I've read that replacing with new halogens can cause problems with melting wires; the lights/turn signals still function, but just not in an optimal manner.

The contacts appear pretty corroded, so I'll definitely be replacing those. Any help will be greatly appreciated!

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Buzz

 

Green Black Stripe is High, Red Black Stripe is Low.

The wires are pretty light gauge, I would have to guess 18, maybe 16 at best? Assuming it is 18 gauge like I think, it should carry no more than 180 watts, and thats on a run 10 ft or less.

The dimmer switch is fed from a single wire of the same gauge, cant recall the color at the moment, at which point it splits off. In terms of wire run I would expect the headlights each to be over 10 ft from the headlight switch. I know when I depress and hold my dimmer I can keep both the highs and lows on at the same time.

Halogen lights draw a bit more current than incandescent (which is why places like LMC recommend the headlight relay kits). Assuming that the Highs and Lows on together is 65w+55w+65w+55w=240w, you have well past exceed the capacity for 18 ga wire of any length along with 16 ga of runs greater than 10ft.

You are probably right about melting the wires, and I would start looking along behind the dash between the headlight switch and the dimmer, or along the left fender. (Probably along the left fender first, bc its a PITA to get to this stuff behind the dash)

In the process of re-wiring my truck Ive used a 15ft standard run for wire capacity, which puts 240 watts / 20 amps firmly into 14 ga territory, and 12 for anything longer.

 

What you're indicating matches up with what the manual says. I am getting that sinking feeling now that there is some melting going on; I dread the thought of getting up under the dash. Maybe in the spring/summer but surely not right now! Way too cold to be doing that at the moment.

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Thanks!