I recently found that the rear, top bulb socket on both sides (& the 3rd brake light up top), were melted. I picked up clean sockets from the junkyard and wired them in.

I do not know what worked prior to as the truck is new to me...as of today:

With the lights off, all turn signals and hazards work perfect.

With the lights on, the driver side signal works great. The passenger does not flash. Now for the strange part, with the lights on, the hazards work fine.

Any initial thoughts?

Thanks in advance.

 

Melting could mean too much current running through the wires/sockets.

I believe the hazards are on a separate circuit than the t/s and they work fine.

The lights run through the multifunction switch, which also controls the t/s, and the corner brake lights run through that also. However, I do not think the 3rd brake light runs through it.

For whatever reason, it seems to make sense to check the multifunction switch and associated wiring.

 

I'd take a good look at the tail light harness itself, hacked into add trailer lights without use of pre-made T harness to do so is a fairly common practice with trucks. Over time corrosion sets in with nothing but black tape protecting splices made.

My 94 recently suffered similar issues and had no blown fuses however same time had no tail stop or turn lights "unless".

Had brake lights if tails where on but still no tails though. Had turn signals if brake lights where on.

Of course it varied a bit from one side to other but you get the idea.

I always used a T harness to add trailer lights to the two I have so never had look at the tail light harness with any degree of detail till the other day.

Got to searching down the problem and found the tail light harness had been tapped into before I bought it right after point it plugs into the main harness and I mean right after that plug. Those connections where all toast, found right side tail light is connected to lic plate light feed wire.
I doctored it up for now so they work but it won't last. Never noticed it was there as someone snipped off trailer wires very near connector covered it with couple wraps of tape.

Not enough wire left after connector do a good solid job repair to it, especially the tail light wire at that point. Literally 1/2" of wire sticking out of connector with no casing left on it to work with. What little is there is also now nice and "black/green" too.

What I would really like is a good used replacement tail light harness (anyone happen have one from a truck they are parting out? I gladly pay few bucks for one and I wouldn't care if damage little bit as long as it wasn't right at the connector).

Anyway if I can't find one and so far no go, junk yards around me don't have them now days after the high price of scrap steel....... but I digress. I'll have no choice pull the tail light harness out bring it in the house, sit down with some wire and solder do best I can to make it last the winter. Likely have to do away with the harness connector completely if I can't find a replacement, won't that be fun! Even just that connector with few inches good wire on it would help.

Aahhh veered off topic there a tad bit there sorry bout that but you get the idea, might not be your issue but surely worth a look see a minute.

 

"Not enough wire left after connector do a good solid job repair to it, especially the tail light wire at that point. Literally 1/2" of wire sticking out of connector with no casing left on it to work with. What little is there is also now nice and "black/green" too."

the shorty wires are a pain. I have fixed a few by polishing up the wire with steel wool (I know there is only 1/2" to work with but the steel wool is usually flexible enough to get "in there") then crimping a tube type wire connector, etc etc. Who knows, if you buy a used harness you might end up with a few of these same type of wire connectors after you start manipulating it for installation.

 

Thanks again for all responses...I've tracked the wiring under the truck and it looks clean. I'm guessing the multi-switch...the wiring under the dash is a mess; I've not yet straightened that out; could be part of the problem.

 

Hey, the dash wiring could be worse... This is what I had to deal with:

 

Quick update: after watching closely, with the lights on, the passenger brake light dims instead of getting brighter when brake is applied. I then turned on flashers...this is funny...the rear lights alternate!

I'm assuming a brake and signal wire are crossed...any other thoughts?

 

Another update: While cruising 55 mph at dusk, I flipped on the headlights; the truck immediately downshifted. I sped up, the truck shifted, I turned off the headlights and tried again. Upon turning on the headlights, the truck downshifted! I repeated a third time to be sure. Any ideas?!? Chance the two issues are tied together?

'96 F250, 460 Auto 4WD

 

Update: I found an incorrect splice where the brown and black wires were crossed for the passenger side brake/turn bulb. Lights seem to be fixed. Have not drove to test "downshifting;" highly unlikely this is corrected.

 

You may not be down shifting, it's probably dropping the torque converter lock up, that is triggered by the brake lights.. Sounds like you may have a tail light and a brake light wire connected somewhere..

 

Awesome feedback! Thanks, now I'm excited to drive and find out if the wiring issue did in fact correct both.

 

Just to close out thread, the crossed wires did in fact correct both situations. It was the torque converter lock-up. Tx to all for input.