Since I’m not at the truck (46), most of The wiring diagrams indicate stop/turn and running options out back, and 2 single filament bulbs…… trying to think it thru why there is even a 2 filament bulb which has offset tits (giving 3 light options)
mine may have a flasher option and does that stand alone, never needed to deep dive on this till now)
Those dual element bulbs are big compared to singles..
I’ll start by checking out how many wires I’m working with…..from the steering column unit and to the back end and in the light.

If the rain continues this week I’ll roll up to the shop….wont take long to be enlightened, fortunately the truck has a complete newer original style harness which makes sorting electric issues easier .

Chuck

Hank: 46 Chev 1/2ton shortbed
2023 Miata RF Club