My uncles truck's headlights recently stopped working, It is a 2006 F250 Diesel.

He says the high beams come on, but there are no low beams.

Does anyone know where to start?

 

Fuse then bulb would be a good starting point

 

Thanks SSCULLY

Will definately look at those first.

Does this truck have a Multifunction Switch? (This is not my truck)
Could a Bad MFS be the Cause?

 

Yes it does have one, but right now start with the basics.

Check the fuses ( there is a L & R ow beam, think in the mid-40s range in the fuse box on the F250s ), if they look good, next remove 1 bulb ( don't touch the glass with your hands ) and check for power at the bulb connector with a meter. should be a black, and 2 color wires ( something like orange w/ light green stripe, don't think that is correct, but you get the idea ).
If you have power, the bulb is bad, if you don't have power that is when to look at something a bit more off the beaten path.

The low beams will be different color wires on the connectors ( L to R ) and the high beam will be the same color ( as well as ground ).

 

SSCULLY

Pulled both low beam light fuses out, they looked good. Then put the fuses back in and tried the lights and they now work. Go figure.
This was an easy one

Thanks for your replies.

 

Dumb question, are the bulbs stock wattage ?

That sounds like heat worked them loose, which in a SWAG moment, I would say is an over sized bulb.

Just a question on why the fuses worked themselves loose.

 

All stock, no mods on this truck

 

On second thought, he recently had an engine control module replaced (if I am saying that correctly). His engine died suddenly and he could not start it. He was always having bad fuel milage, now it's normal with the replacement.

This was done at the dealer under his extended warrenty. Maybe they did something.

 

OK, that might explain it. Fuses "usually" do not come loose, unless heat / cool cycles are above normal, or human intervention.

In this case, keep it in mind if something else stops working. Pull the fuse and reseat it. Once again, good job by those Ford mechanics