[Z15]

I recall my 99, 01 and 04 all came with a jumper harness to use for trailering. It was in the glove box and I was told you needed to use that harness to have trailer brakes. I never used them and threw them in the glove box when I traded. The trucks all had the HD trailering option with the 6 pin connector at the back bumper.

If you bought the trucks used, the previous owner may have kept the harness or is was pillfered.

btw-My 2008 did not come with any jumper harness so it must be wired differently.