I'm adding delay wipers and I think I'm having the same problem I had when I undertook this endeavour with a 78 Corvette. The truck is a 78 GMC and never had delay wipers. I added the switch and the delay box but still no fun. Everything works but the delay. I read in the 78 shop manual that a wire plugged in to the ACC port in the fuse box. Can someone tell me what color wire does this splice to? I'm assuming this feeds power to the delay mechanism. On the 'vette, I had the same issue until I figured out I needed a special wiper motor cover and needed to splice a wire coming from this cover into a green wire.