I agree with 53 4 me, but one word of caution. I just rewired my truck using the Chevy Duty wiring harness. The directions are cryptic, to say the least, and you really have to pay attention to what you're doing. Furthermore, the harness is for the stock setup, so if changes have been made, those changes may throw you off.
For example, my truck has two horns mounted on the right side of the firewall, fed by a relay. The original horn was mounted in front of the radiator, without a relay. It took me a little time to figure out how to get the horns working again.
The original truck didn't have turn signals. If those have been added, you'll have to figure out how to adapt the wiring to fit your setup. I'm not saying it's impossible, just warning you that it ain't a 2 hour job. It'll take some time to get it right.
I was also changing my gauges, so that added an extra kink that I had to figure out. It's all done now (except the headlights because I'm cleaning the "buckets" up and painting them before I put them back together) and a couple of odds and ends.
BTW, the Chevy Duty harness worked out really well. It even has some extra wires you can use if you have (or want) turn signals.
