Troubleshooting A Trailer Wire Harness That's Only Reading 4 Volts At The Trailer Connector

Question:

Hi, I can only get 4 volts coming out of the 4 prong harness. The T-connector has a good ground.

asked by: Mike C

Expert Reply:

Hey Mike,

If you're getting low voltage at the trailer connector of the T-One Vehicle Wiring Harness # 118613 then it's typically going to be a power or ground issue. Since you've stated you already have a good ground checking the power will be the next step. There should be an inline 15 amp fuse that you can remove and check for any damage. The inner band that goes through the fuse could be slightly damaged but not fully blown causing the issue. From there you'll just want to test the power wire after the fuse and then right before the ModuLite. If you're getting 12 volts leading up to the ModuLite but not right after it then we know it's faulty and the wire harness just needs to be replaced.

If you are getting 12 volts after the ModuLite but not at the trailer connector then you have a short somewhere in the wiring between the two that will need to be cut out and replaced or you can replace the whole harness.

Let me know what you find and we can keep troubleshooting further if needed.

expert reply by: Kevin C

Mike C.

5/30/2024

Thanks. It turns out that the module was bad and only putting out 4 volts. This is the second module that has failed in the last 4 years. The first module just went complete open circuit.