I recently bought a 3 prong fog light switch for my 76 which ought to light up in the center. However, the old switch was only connected with 2 wires. Using those two the new switch lights the lights but not the knob. I cannot find a wire with an unused spade connector to attach to the third prong. Where should the third wire to light the switch originate from? Wiring is not one of my strong points.

Third wire is a ground.

Here's what wires should be there:

Click to view attachment

Can't make out the word before red.

Grey/Red

Thanks

The grey/red wire is the one I can't find. Would that come out of the harness along with the black/blue or from somewhere else?

If your fogs light up now you don't have to worry about the gray/red wire. See the diagram below. The only wire needed for the light in the switch is ground.

K17 would be the bulb? That's a nice diagram.

Thanks everyone! Very helpful.