Sender is not voltage specific. There is no juice to them. Who sold you a "12V" sender? Just need to have a 30 OHM rating,
1. DO NOT run ANY voltage to the sender.
2. GMC's had positive ground.
3. Gauge has two terminals, one for voltage and one for the sender.
4. If you don't know about wiring, seek help here before wiring.
5. On your truck, the fuel gauge "frame" needs to be grounded. Probably has a lug or brass plate to touch dash metal when tightened up,
6. The sender terminal on older Chevy gauges is on the "F" side of gauge and may have a red warning tag.
