Tap switch hookup:
The directions from GM include a drawing with the appropriate resistor values to make the tap switch function. They are correct as mine works perfectly. I had a large box of resistors and was able to come up with almost the exact values that GM asked for, I used 1/4 watt. GM’s drawing uses two single pole, single throw switches. I made up a diagram using one mini switch which is a DPDT (double pole, double throw). It is momentary and is a center off switch. It cost a couple of bucks on eBay. I mounted it on my dash where I can reach it easily. I simply reach up and tap the switch lever up or down, it’s small and hardly noticeable.
My tap switch wire was in the harness near the bulkhead connector. It was labeled as “tap switch”. I just added more wire and ran it inside the car and under the dash.