When I did mine I feel like I had the same problem and turned out the location where I spliced into the harness was the problem. The main harness “y”s off if you will under the seat. I had picked out the correct color markings and spliced accordingly but I spliced into the harness on the right side of where the harness goes under the seat, so toward the back of the truck. Mine did not work and I had checked and rechecked like you and with nothing. Not even sure what made me move it but once I spliced back into the harness on the left side of the “y” it worked.
Not sure if that’s your problem but hope that helps