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Weird electrical issue with trailer

Hi, I have a 97 Ranger that is COMPLETELY FINE as long as it’s not towing my trailer. All the lights work properly. When I hook it up to the trailer, the lights on the truck still work, but I can only get 4-way flashers to work on the trailer. Obviously, the problem is in the trailer, right? Well, when I hook up the same trailer to a different vehicle, everything works fine. (The only issue when I towed the trailer with another vehicle was that the wheel well running lights would turn off when I applied the brakes.)

Also, when I am towing this trailer with the truck, the clock on the radio goes out whenever I brake. This does not happen unless the trailer is hooked up. The radio clock comes back on again when I let up on the brake. If I brake and then put on a turn signal, the clock comes back on. Weird, huh?

I would suspect a fuse, but obviously if a fuse was blown the lights on the truck itself would not be working. It’s acting like there’s not enough electricity in the truck to power everything at once. I’ve tried spraying some electrical connection cleaning product in both the male and female connections, and tried swiping out the female end with a nail, but no luck.

Any luck? Thanks.

Sounds like a possible grounding issue to me. Check your grounds, start by tracing the ground wire from your harness on your truck. Check the ground connections on the trailer lights as well, you may have a bad ground on the trailer as well as the truck.

Sometimes when Wiring harnesses are spliced in the connectors they use allow moisture in and eventually you have corrosion.

If there was a loose connection to a circuit that powered both the radio clock and the brake lights, that symptom could result. Also if those circuits shared the same ground and it wasn’t solidly connected to the chasiss I think that symptom could result. What I’d be inclined to do if a quick visual and little DVM probing around didn’t expose the problem, I’d make up a test jig to connect to the trailer wiring connector. I’d connect bulbs between the various terminals and measure how the voltages are affected.

The clearance lights on the trailer are clearly wired incorrectly.

Are you using the proper wiring harness on the Ranger? If it has separate brake and turn signal lights, you need a converter to hook up to a standard trailer harness.