The trailer lights aren't working right when I plug in a trailer to my '89 suburban. I was going to start investigating, but do you know what the person that spliced it in would have spliced it into? Maybe that's a dumb question, but I mean did they likely just splice into the tailight/brakelight wires??

Do you know what all 4 wires are on the 4 pin harness??

thanks!

Yellow left turn and stop green right turn and stop brown tail lights and white ground when they are spliced they are spliced into the respective wires in the tail light harness (they arent the same color) but on most later model trucks there is an adapter that you put in the tail light harness you just find the plug at the rear of the vehicle that goes to the taillights and unplug it, put the adapter in between the two ends and plug it back in. in some cases the trucks came with the four wire harness already under there just tied up with the harness. you can use a test light to check the truck plug just turn the key on and try the headlights and put the light on the brown wire then try each turn signal and use the test light on thier respective colors in the plug. 99% of the time I have trouble it's with the ground. I usually just use a self tapping screw and screw it right to the frame at the rear of the rail. if the plug checks out it's time to check the trailer hope this helps.

will check it out hopefully this weekend. thanks for the tips.

lots of times its just a matter of cleaning up the connections // i take a small piece of 100grit sandpaper wrap it into a cylinder and twist it inside the ttrailer plug to clean up then spray with wd40 same thing on the trailer plug also good to check light bulbs in trailer