Troubleshooting Trailer Brake Lights and Turn Signals That Are Not Working Correctly  

Question:

Expert Reply:

The two most common causes for problems with trailer lighting functions are corroded vehicle or trailer connectors and a bad ground on the trailer or vehicle. The good news is that these two problems are fairly simple to check and correct.

First, check that the main trailer connector ground wires on both the vehicle socket and the trailer plug are solidly connected to a clean bare metal surface that is free of grease, rust and paint. A weak ground can cause all sort of odd behavior from the lights. You can move the grounds to new fresh metal surfaces on the truck and trailer if necessary.

Next inspect both connectors inside and out for any signs of corrosion - including even slight greenish or whitish discoloration on the contact surfaces. If your vehicle 7-way is corroded you can replace it with a part such as # PK11893 that fits Ford, Chevy, GMC and Nissan OEM sockets. If your trailer 7-way plug is corroded and needs to be replaced you can use part # H20044 along with a junction box # 38656 to make your splices. You'll need ring terminals like # 44-5310A and # DW05702-1 to make those connections.

A have also linked for you an article on troubleshooting trailer wiring.

You can also test the trailer directly when it is not connected to the tow vehicle by applying power to each circuit on the trailer plug. This will tell you if the issue is in the vehicle wiring or in the trailer wiring. You can use any 12V power source such as the vehicle battery or a spare 12V battery to apply power to each circuit one at a time.

expert reply by: Adam R

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