Thanks George. I stand corrected. Dual filaments on outers. I even have a 1960 GMC but it's all apart.
Cathy: I just checked the 1960 wiring diagram. Hope you have one for 1961.
Just as George says. 3 pins on outer bulbs, 2 pins on inner. The ground is done by wiring the two driver side bulbs together and to ground, and the two passenger side bulbs together and to ground.
The high beam is done the same way, as driver and passenger pairs. The diagram shows one high beam wire and one low beam wire coming from the dimmer to a dash connector (I believe you might call this the turn signal connector), then to a smaller 2-pin connector, out of that connector/block with 4 wires to bulbs. (If GMC wiring is the same as Chevy)
I'm guessing that there is a miswire from that last 2-pin connector or in the "chain wiring" of bulbs.
