Backup/reverse light - 3 wires?

[juno]

I am doing a shell-on renovation of a 1976 Airstream Sovereign 31’, and currently rewiring the exterior lights. The only thing I can’t figure out is the backup light — there are 3 wires from the can: Yellow, Brown, and White (riveted to the can). The yellow and white I get, but what’s the brown?

The original manual only shows a power line and ground. The bulb socket is a 2-prong type, and the bulb has 2 separate filaments. I can’t imagine why there would be 2 separate power sources to the reverse light. Do the brown and yellow both get spliced together?

[BayouBiker]

Just a guess, is yellow for backup and brown for license plate? Usually the filaments are two different brightnesses. Does it dual purpose?

[88Limited]

The wiring diagram in the book for my '88 says the yellow is for the backup light and brown is the stop & right turn signal. Not sure why it would be wired up to the backup light. I have my cans out now cleaning up the bezel, I'll look at it tomorrow and see what I can see.

Edit: interestingly, according to the diagram you posted there isn't a yellow wire, reverse should be black?

[Wazbro]

Current standard is brown=running light, yellow=left turn/brake, Green=Right turn/brake, purple=backup lights.
Are you that is backup can , not left turn and running light?

[tbashin]

Looks like 4 wires in the pic and one is black which per your diagram is the reverse light.

[juno]

Definitely the backup light -- the cover has a clear center, though it's possible that a previous owner did work on the lights and changed the order, but when I took out the old wiring, the yellow wire was connected to the backup light.

I don't have the bulb with me currently, but here's another image from the front of the can, and the wiring color scheme that matches my TV and new 7-pin plug.

The manual diagram lists the backup wire as "black," but the 7-pin wiring diagram has two different options, one for US and one for Canada, where the colors are different (I bought the trailer in Canada).

It would make more sense for this can to be used as a turn signal/brake light. I'm swapping out the existing wires anyway (they're mightily corroded), so I can use it for any of the taillight options.

[Wazbro]

With these lights the outside is ground the 2 contacts are both hot. Maybe they had both filaments for backup lights?