Jon D,
Without going into specific troubleshooting, I will say that there is a wonderful Tech-Tip by "cletis" dealing with turn signals.
Between the instructions supplied (I hope) by Chevy Duty and Cletis's tech-tip article, you will be blinking in no time.
Lots of folks will probably be along soon to help with this problem, but reading the tech-tip first might answer some of your own questions.
Stuart
