1975 F250. My left rear running light is always heating up the red lens and causing it to bubble. I've traced the wires and changed to a good socket, and replaced wires that were frayed or damaged, but the problem continues. I'd like to fix it once and for all. I was hoping that someone more knowledgeable than myself could lead me through the process. I have an amp meter, but am a beginner using it. Thanks.

 

Sounds like either the wrong bulb, or there is a fault in the wires or more likely the socket causing the higher wattage brake / turn signal filament portion of the bulb to burn with the much lower wattage tail / running light filament. Brake or signal lights typically are expected to burn intermittently ... unlike continuous burning tail lights.

Your truck uses 1157 bulbs, the thick filament is the brake / signal side is 26.9 watts, the tail or running light portion is thinner and is but 8.3 watts. The bulb is close to the red lense in a small space, red absorbs heat energy of light, 26 watts will get hot in there if continuous. I have fog lights that are just 37 watts in sealed beams, they get warm too.

Part of the socket is plastic and the slots for the two nubs are plastic, the nubs on the bulbs are staggered so the bulbs should only go in and twist in the proper orientation, but in time plastic can get worn or damage by ham fisted people forcing bulbs in wrong. If ever replaced, might be the socket was made too large in manufacture, allowing a bulb to be inserted and twisted in place 180 degrees wrong.

I know you said you used a new socket, but if connected just exactly like it was found, might be you just duplicated a old goof. It could be the a socket was replaced in the past and the two hot wires reconnected in splice reversed?

I would look closely at the bulb, try some small jumpers to school myself on exactly which base contact lights which filament, then make a note or chart of how the locator nubs relate to each base contact, then use my grounded test probe and ascertain that the correct contact in the socket is 12v hot when either a signal or tail light is used. I use park light switch for the one, and the 4 way flasher for the hotter side so no need to have a helper.

 

Correct, that's the only thing it can be. there are several possible causes but you're lighting both elements in the bulb and it can only take that much heat so long.

 

Some of the new sockets wiring instructions are labeled wrong, including the ones from big name suppliers. Are you using genuine Ford housings? Can get pretty hot down south setting in traffic with both elements illuminated and don't remember any lense problems. As above maybe wrong bulb. Just asking.

 

I wonder if you drilled a small hole below and above the bulb if it would vent enough heat to stop distorting the lens? You'd probably have to glue some screen over it to keep bugs out of the housing.

If the wiring checks out ok, get LED bulbs. They burn alot cooler.

 

Thanks guys. I will try to change socket again. This has been an issue for more than ten years. I have flipped the wires and traced brake light wire/running light wire, etc. It seems to be sorted out, so, I install a new lens, and a month later I notice that the lens is melted at the blub.

I have tried all the procedures etc. you guys mentioned, and the problem is alive and well. That's why I posted. It's got me scratching my head. Thanks again.

 

Are the bulbs burning out ?

 

Are the lenses OEM Ford or aftermarket? Could the wiring /circuit be fine and the lenses are just an inferior plastic that can't handle the heat?

 

Speedfreak78: I'm not sure. Been in garage so long that where they came from is lost.
Mark a: The bulb is not burning out.
440 Sixpack: That could happen when the brakes are applied. I'll ck. Normally, I have running and brake lights. I continue to have the running light and brake light burn when they are supposed to. I'll ck to see if both are buring simultaneously.

 

At night / dark if you turn on the running / tail lights is that side brighter than the other side?
If so its wired wrong.

When ever I have to re-wire a socket like tail / turn I test to make sure I have the right wire going to the right part of the bulb.
I turn on the tail lights and I use that wire and test each socket wire.
1 should be bright (brake / turn) and the other a little dimmer (tail / running) then hook that wire to the right side of the socket.

What happens if you swap bulbs side to side dose it still melt?
Dave ----

 

Perfect. Good solid How-to. I'm on it. One note, however, is that this only occurs on the driver's side, and at night I can see that both the passenger and driver's side running lights are illuminated with the same brightness. Brake light comes on and turns off with the pedal, and does not stay on. I know this sounds impossible. But I test the taillights every time I change a bulb or a socket, or mess with the wiring at all. Running lights illuminate the same intensity left and right. Brake lights come on brighter on both sides. I change the lens on the driver's side b/c there is a bubble in the red lens, and the next time I look, the new lens is distorted and bubbled in the same spot.

A couple of years ago I changed the turn signal mechanism in the column. That meant trying to match new bright wires with old faded ones, and trying to get all the colors correctly matched. Something must be amiss there so that when another circuit is activated, the brake light activates as well. That's is the only possible explanation. "When you've eliminated all possible explanations, whatever remains, however improbable...."

 

No, the bulbs are not wearing out.

 

1. Check all above suggestions and still get no where.
2. Swap to LED bulbs, at least you will quite burning up lens.

 

The only cause there can be is the bulb is getting too many volts. period.

Test the voltage to each terminal in your socket to the socket ground, and then to the pickup bed. for a ground. if the voltage checks out it's the socket, if it doesn't work forward.

I've found most of the time it's the socket.

 

It does read like a bad socket is in the mix. May just be wired wriong ... or maybe has an internal problem.

Actually, just about all the bulbs get the same voltage, but some bulb filaments are fatter and thus create a higher amp load ... volts x amps = watts. Bulbs are rated in watts. The only bulbs I can think of that don't get full voltage are instrument bulbs when turned down by the light switch **** being turned.

It's easy to swap in a new socket and once wires are clipped loose from the old one, it's easy to accidentally wire the new one in with reversed hot leads. The tail light socket has three leads ... one is brake & signal ... one is tail ... one is the bulb ground.