I have an '98 F150 Flareside. I recently replaced the upper bulb (stop and turn signal) in the tail light assembly and while verifying correct operation, I noticed that the lower bulb in the tail light assembly (a 3057K dual filament bulb) only illuminates the minor filament (I've tested the bulb and both filaments are OK -- both sides).

I am curious why a dual filament bulb (3057K) is used when only the minor filament appears to be used, or should I be looking further to determine if there is still a malfunction?

Anyone have thoughts on this?

 

I'd have to guess that a previous owner installed the wrong bulb and, since it "worked", left it in there.

Steve

 

I am the only owner. This is the first time the tail light assembly was taken off the vehicle. I also know it's the correct bulb, as the bulb # is stamped on the interior side of the tail light assembly.

 

Dumb question of the day ( or at least my first for the day ).

I think the SCrew has the same style tail lamps, and thought there was only 2 bulbs ( again been some time since I had a '01 MY out ), S/T/T bulb and reverse.

Also the Owners manual bulb guide ( page 206 )
Rear turn/sidemarker 2 3157NAK

Quick question, how many wires and what colors are they, that go to the socket in question ?

 

Yes, I saw that in the manual about the 3157K. I believe the 3157K is a compatible replacement for the 3057K and 3457K. Some bulb replacement guides will identify the 3157, but will note as well to match existing.

I've contemplated taking the tail light assembly off again and inspecting the wires, but wanted that to be my last resort as the wires are all taped up now and I didn't want to interfere with the factory taping so as to maintain the integrity of the environmental protection that the factory tape job provides.

The tail light assembly has 3 bulbs in it which currently function as:

• The top bulb is a 3457K which is tail light (minor element), brake light and signal light (major element).
• The middle bulb is for backup indicator
• The bottom bulb (the one in question) is a 3057K and appears to also be a tail light (minor element).

As per my previous post, the housing that the bulb assembly fits into has the matching bulb part number molded into the plastic. That is 3457K on the top, and 3057K on the bottom.

I also reviewed the wiring schematic in a Haynes repair guide and I can't find anything in the circuit that would represent the major element of the lower bulb.

Behaviour for the lower bulb is the same for left and right. Also, unlike the socket for the upper bulb which shows signs of discoloration from the heat of the major element, the socket for the lower bulb does not show any discoloration at all, reflecting to me that it is highly probable that the major element has never been activated on the lower bulb.

This may be absolutely normal for this model of truck, but I still find it interesting that a dual filament bulb was used for a single filament role. I also find it interesting that a different bulb part # would be used for a bulb whose minor element provides the same function as the minor element of the top bulb. But then again, anyone who has owned one of these trucks for a while has encountered a number of things that ford designers did that defies certain elements of logic or reasoning.

 

Ok, got the 93-3 ext lamps uploaded.



Notice the center area, that shows an additional bulb with the other, that has a light green wire to it, that is not used.

I don't know if this is what you are going to find if you look at the bulb connector.

I wouldn't worry about taking the tape off, just re-tape it with some 3M cold weather tape ( Home Depot, on a blue card ) when it is 30* or higher, and you will have just as good a loom as the factory. All the factory tape is doing is holding the wires together, it is not offering any additional weather protection than the insulation is.

If you want to, I cut the end towards the truck's harness and tie it to the turn / brake circuit on the other bulb, to double the light output. That would be 2 x 21W rather then 1 x 21 W.