1977 Chevy K10 Printed Circuit Question

[ray_mcavoy]

Although the printed circuit has traces leading to that bulb location, they weren't actually used for the 4 wheel drive indicator light.

Instead, the 4 wheel drive indicator light uses a bulb socket with it's own wires. If you look around in the dash you should find a bulb in a plastic socket with 2 wires (white and brown with a white stripe according to the factory wiring diagram).