2005 F250 Supercab Lariat, 5.4 V8, 37k miles. With auto lights.

I got an odd one. I just bought this truck a couple weeks ago so I don't have the shop manuals yet or wiring diagrams (coming soon). I noticed the LH (driver's) high beam was not working. Both low beams work, but when I flip to high beams only the RH high beam works and the LH headlight goes totally dark (parking light stays on as it should).

I figured it was the bulb, so I replaced it without testing anything and it still has the same problem. Doh! I know - always verify before replacing a part, but I figured it was obvious...

Here's what I found - 3 terminals on the bulb connector. On the side that is wokring correctly, I get +12v from the right hand terminal to both the ctr and left terminals. In high beams I get +12v from the left hand terminal to both ctr and right terminals - basically it appears to flip from one side to the other, more or less.
----
On the BAD light,
Low beams: +12v from Bl/W to Bk wires, and +12v from Bl/W to Gr/Bk. Looks the same as the good side.

High beams: +12v from Gr/Bk to Bk, and nothing from Gr/Bk to Bl/W

So it seems I should get +12v on that last pair, but get nothing. Is there a relay or fuse that would be out? Seems odd for only the one light, but I suppose it could be one bad terminal of a DP relay. The Bl/W wire is clearly connected to something since it shows voltage in low beams.

Any clues?

Thanks,
Dave

 

check fuses think they are fused indivigually

EDIT:guess low beams are fused separate

 

Fused individually? Weird. ...But OK. I ran out of daylight before I got to checking fuses or relays, but I'll get to that tomorrow. Thanks for the tip.

 

Check the right rear tire's pressure and switch to synthetic turn signal fluid.

 

Yes there are 4 headlight fuses, separate for each side and high/low. If its blown you have the possibility of a wire short somewhere, unless they were running higher wattage bulbs.

 

I looked in the owners manual and it shows separate 10A fuses for L&R low beams (#46&47) but High beams only have one 15a fuse (#30) listed. There is another fuse (#7) that is a 30A and is labeled "high-beam headlamps, flash to pass". I'll check these out, but am not seeing a L&R in the manual for high beams so far.

Thanks,
Dave

 

I checked those fuses both visually and pulling them for a continuity check and they are all fine. Double checked the owners manual and see nothing else in either fuse panel that says it relates to the high beams or headlights. I also did a visual scan of all fuses in the panels and saw nothing blown.

Only other thing I noticed under the dash was the previous owner had tapped into a Gr/R wire going to a large white plug on/under the steering column, probably for some accessory, but the wire had been cut off and was just sticking out of the little tap connector. Doesn't seem like that could be the issue.

Any clues? I think I'm going to need a wiring diagram here, to get much further with this.

I'll do a little more voltage investigating tomorrow when I get another chance, but I'm not hopeful it will get me much farther without a wiring diagram.

Thanks,
-Dave

 

Follow-up: Fixed it. Now that I had a bit more time to look into it, it appeared I was getting the correct voltage at the connector pins as called for by the switch positions, so I started to suspect the connector. Pushed and wiggled it around while on high beams and the light flickered on. So I bent the high beam connector tab a bit and now it seems to work fine. From some other evidence I see from looking around, it looks like maybe the truck had been in an accident on that corner in the past and perhaps that lead to the connector issue. It must have been some time ago as there is no residual paint smell, and that smell sticks around for a while, from experience.

Thanks for the help.

-Dave