Taillight assembly

[Drought Buster]

So in the 3 light assembly the inside lamp is a turn signal and brake light, the middle is a reverse light, and the outside is an 1157 bulb. What does this light do other than a taillight?

[TG Twinkie]

The 1157 bulb is a dual filament bulb. It is both the tail light and the brake/turn signal.
A close look at the bulbs filaments and you will notice one filament has a finer (smaller) gauge. This is the tail light. The filament closest to the top of the bulb has a heavier (larger) gauge. This is the brake/turn signal.
There should be 2 wires coming out of the base. You can test which is which with a 12 volt power source. The brighter one is the brake/turn signal.

[Drought Buster]

That is what I was thinking. The brake light isn't working on either side, so that gives me a place to start.

[Drought Buster]

Upon further inspection there is a wire that has either been cut or broken. This evening's project. Thanks for your knowledge!

[Drought Buster]

Any idea where the yellow wire goes?

[Slats]

I've always heard that yellow, containing the letter L, is for the left turn signal and green, containing the letter R, is for the right turn signal.

[cliffcharb]

Yellow is generally back up lamp

[Drought Buster]

It looks like the yellow was never hooked up.

[Drought Buster]

I don't see where the yellow wire should go.

[TG Twinkie]

Is the yellow wire connected to the light fixture?
Check to see if it is the brake/turn signal or the tail light by connecting it to a 12 volt source. If it is the tail light just connect it to the fixture on the right in the photo. Were you see the wire nut.
If it is the brake/turn signal you are probably going to have to do some digging in to the wire loom.

[Drought Buster]

It is for the brake light. The tail light works. I'll have to dive into the wire loom it seems.