sammyg

Yes,trailer harness on the truck is factory. The last time I pulled the trailer before this trip,I could not get any lights on the trailer to work using the 7 pin round connector.I found corrosion on the contacts on the wire loom itself and had to end up using the 4 flat connector. I'm guessing that corrosion in the factory wire loom may be the culprit.But I am not sure. And yes I did use a multi-meter to test the trailer lights.

JByrd825

Hey sammyg, I have a test for you. With the trailer hooked to your truck, turn on your headlights on in your truck so that the running lights on your trailer Illuminate. With everything on, check to see if your center high-mount brake light comes on. If not, try the left blinker and check. Same thing for the right blinker. The reason why I ask, is that the factory harnesses for these trucks have multiple ends that are capped off for the trailer plugs. There should be a lead for "third brake light" and "reverse lamps" that may not be utilized on the 7-way plug but are present in the wire harness for different applications. It's theoretically possible that they may be corroding and back-feeding from being plugged into your trailer. And if your sockets are as corroded as you said, replacing them is the best thing to do in this situation since they can cause back-feeding and shorting issues.

sammyg

Thanks, it's raining pretty good here today,but as soon as I get a clear day I'll try that. Many thanks to all who offered advice,as I said ,never was much good with automotive electrical issues so every little bit of advice helps.