First let me say thanks in advance for any help. I have an 04 Lariat SC, a week ago while driving home I attempted to turn on my high beams. The headlight went out, returned to switch to low beam and they came back on. I have checked and rechecked all my fuses, none blown. Anyone else had, or having this problem? Again thanks for any help or information I get on this issue.

 

Which fuses did you check ( all does not tell too much, if it really is all, why are you checking the radio fuse ) ?

How did you check the fuses ?

Any modifications to the truck ?

Do the highbeams work on the FTP mode ?

Have you tried new bulbs ?

 

I checked the fuses realted to lighting in both the fuse box in side the right kick panel, and un sure of which one to check in the power distribution center under the hood I checked them as well. First I tried the simple test of making sure there is power to both sides with my test light. When They all tested ok I pulled them out to and visually checked them to make sure. And I am not sure what FTP mode is, so I can't answer as to if they work then or not. I have not tried new bulbs, thought I would check here and see if the fix was more complicated then that. And in the case of lighting modification the answer is none on this vehicle.

Again thanks for the time spent, and your help.

 

The Aux fuse / relay box under the hood should have nothing pertaining to the headlamps ( that is 4x4, AC, DRLs and clock spring illumination I do believe ).

The fuse you are concerned with is F35. You know the power to the main headlamp switch is good, due to the parking lamps and low beams working.

The FTP is Flash to Pass mode, or when you pull back on the MFS.

If you want to be sure, use a meter and check the bulb connector for power when you have the high beams on ( MFS pushed forwards ).

Simple enough to check.

High beams are a single fuse to both sides, it is the light green w/ black stripe wire into the bulb connector. Ground at the bulb is the black wire, else there are the ground lugs in the inside fender for the other side of the meter.

Let us know what happens with the test to the bulb connector.

If you do not have power there, next we will need to check the high beam relay socket for power to it ( from the main headlamp switch ) and bench test the relay. That is pending what happens with the bulb connector test.

Occam's razor, the simplest theory is the better one.

 

ftp doesnot work and high beams do not work. low beams are fine. checked fuse 16 in interior box and it was okay, i went ahead and replaced the fuse anyway. What the next step?

 

Check for power at the bulb connector, to see if you need new bulbs.

It is the pin in the connector that has the Light Green w/ Black stripe on it.
The other 2 wires are :
Black ( ground )
Dark blue w/ white stripe & Dark Green w/ Orange stripe ( low beams left & right )

 

Does the high beam indicator in the cluster go on or off? If not, then the problem isn't at the headlight bulbs. If it does, then it may be.


Or you can half-split the circuit.

Pull F16 and check for power one terminal of the plug when the high-beams are on. If so, the problem is "downstream" from F16. Im missing from both fuse terminals, then the MFS or its connector is suspect.

 

Good point, sometimes hoof beats are zebras.

I completely airshot this one last night

 

Well damn my luck I got this exact same problem now. I was driving down the gravel road to work tonight topped a hill and my high beams just shut off.

Tails and front parking lights work in all modes.
Low beams work in all modes.
Driving lights work in all modes(I did the override mod)
High beams do not work at all but the dash light does.
FTP does not work but the relay is audibly clicking.
Fuses F2.35 appears visually good but I can't electrically test till I get home.

I'm at work right now so I can't do much. Going to get a bit to eat and play with it before coming back to work.

I'm thinking the high beam relay may be bad since it's the most likely. Anyone got the part number for it?

 

Worth a check.

You can pull the Full Size Ford ISO relay, and jumper the contacts or swap it with R05, the trailer tow adapter battery charge relay.

This will have the high beams on regardless of the main headlamp switch or MFS position.
This will not test the fuse, as it is in between the relay and the bulbs.

To jumper the normally open contacts :


If you want to test the signal from the MFS, check the pin marked 86 for power when the main headlamp switch is on, and the MFS pushed forward.
To confirm pin 85, this should be <5 ohms to a known good ground ( ground lug in the lower left hand corner of the fuse panel, down by the carpet ).