O/T HEADLIGHT PROBLEMS 2000 FORD F 350.

Hello out there . I need some help figuring out the headlights on my tractor hauler. Started about 2mo ago had all the lights but low beam. So I replaced the headlight switch and nothing. Did some more checking and found that the turn signal switch runs all light functions,so I replaced it. Well that got me low beams again. Fast forward to this morning turned on the lights have everything but low beams! I'm having a hard time believing it's the switch again and not so sure the old was bad. I'm finding out that this is a common problem with the super duty style truck. Any of you experience this? Trucker

I don't know that vehicle, but could you have a bad relay?

On power from the Headlamp switch is sent to the multi-function switch (aka turn sig switch). The same wire from the headlamp switch is used for high or low and thats decided by the multi-function switch. The low beam circuit leaving the multi-function switch splits and goes into the fuse box under the hood where both headlamps have their own fuse.

I hope I have enough detail for you. The way I see it is the only thing that seems related to both headlamps being inop in low beam only is the multi-function switch. With the exception of a possible wiring problem between the switch and a splice before the under-hood fuse box. One more thing I would check that can be easily overlooked. Unplug multi-function switch and look into the connector ends, make sure the locking tabs for the wiring pins are there and the wires are pushing out of the connector. If so you can use your own judgement on keeping the pins in the connector shell but those connector shells can be bought from the dealer or most auto parts stores.

I have an 02 F350 and an 04 Merc Grand Marquis. The truck lights have never failed, but the ones in the car quit low beams while I was 50 freeway miles from home at night. There is a light computer that coordinates all the lighting. The truck may have the same thing. On the car, the lighting computer crapped out from the many hours the low beams had been used. I found this was very common, even including the police cars. Check Rock Auto's website for that lighting computer application to your truck. In the car it is located close to straight up from the gas pedal by the toe of your right foot.

HTH

Paul in MN

There is nothing technical or fancy with the headlamp circuit on this truck, no lighting control modules or relays. The only exception would be if the truck has OEM daytime running lamps, if this truck has DRL's the low circuit simply passes through the non activated DRL relay (w/headlamp switch on). If the DRL relay is activated or stuck on you should still see the low beam lamps come on but the DRL resister would make the lamps glow dimmer than normal.

There is a main fuse (#13, 30a under hood) feeding the headlamp switch for controls, multi-function switch gets input from H/L switch, then wire leaves the multi-function switch and goes to the fuse box (under hood), this circuit branches into 2 individual wires before the fuse box and each low beam headlamp has its own fuse (#9, 10a LH & #11, 10a RH under hood). The circuits leave the fuse box on individual wires to the bulbs.

If you have a test light or volt meter then check these wires, There is a Red/Yellow wire going into multi-function switch, this should have power with the headlamp switch on. For low beams there is a Red/Black wire leaving the switch to the fuses for the bulbs. For high beams or "flash to pass" the Grey/Orange wire should have power leaving the switch. Also the #9 and #11 fuses in under hood fuse box should have power when low beams are selected.

Sorry for long post, I hope it can help diag.