Is there a fuses or relay on the trailblazer 4 the trailer brake lights. All the ones under the seat and hood are good
trailer brake lights on 2003 Chevrolet Trailblazer
According to my wiring diagram, If your 2003 Chevrolet Trailblazer has a factory trailer wire harness the circuit for the trailer brake lights does NOT show up in the trailer connector! Here is what I found. Pin A - Light green wire, back up lights. Pin B - white wire, ground. Pin C - dark blue wire, "blunt cut" in harness. Pin D - dark green wire, right turn signal, Pin E - red wire, battery power. Pin F - brown wire, parking lights. Pin G - yellow wire, left turn signal. The light blue wire for the brake lights is "blunt cut" in the wire harness and does not go through to the connector. All told there should be 4 "blunt cut" wires in the trailer harness. Where they are cut I can't say. One cut wire is orange and comes from the ELEC BRK fuse under hood. It's cut mate is dark blue and continues to the trailer connector - pin C. The other cut pair is your brake light wire - light blue, and It's mate (black) which is ground. You can do one of two things to get brake lights to your trailer. 1) Connect the trailer brake lights directly to the cut pair (light blue and black) - power and ground, This could be done through a separate plug. 2) Connect the cut light blue wire to the cut dark blue wire which will then bring your brake light circuit to Pin C of the connector. You can then wire your trailer connector accordingly. I know there is a lot if information here. I think it will help you to draw a picture of the connector as I have described and then start looking in the trailer wire harness for the "blunt cut" wires. Good Luck!