Troubleshooting Right Brake Light Not Functioning on a Trailer when Tail Lights are On

Question:

Have 95 Nissan P/U Have checked Trailer lights , New Light assemblies on Trailer . Ground OK on trailer and each light works when you power up each Terminal on flat lead, With trailer connected to truck , tailights work OK and Left side brake and Turn signals work properly . The problem is when tail lights on RR ight side Brake light comes on But Dimmerand if I turn the right side turn signal on the light wont flash . I dissconnected truck from trailer and checked the flat lead from truck using power probe dont have tester ground OK, tailight OK, Left brake light OK , Left turn signal W/ Brake on I get A solid flash , If I check The R. turn I get a flash on and Off If the brake is ON W/ turn signal The Right turn light Just Get Brighter and Dimmer never completely cycling on and off Replaced this unit last year took care of the problem for 6 months Then problem cam back Any thoughts Help would be appreciated Thanks

asked by: Steve E

Helpful Expert Reply:

If I am understanding you correctly it sounds like when you test your trailer with a 12 volt power source all of the tail light functions work correctly, but then when you connect the trailer to your tow vehicle is when you see problems.

If this is the case then it sounds like the problem is on the vehicle side of the wiring and the trailer is good. You could further confirm this if you wanted by trying a different tow vehicle to see if the problem persists or goes away.

One thing you could try to is have the engine running on your 1995 Nissan Pickup when you are testing the trailer lights for function. If you have the engine off, and the taillights on when you are testing you may be drawing too much and that is why the right turn signal does not seem to function correctly. If your vehicle is running the alternator of the vehicle will ensure that the battery can put out enough amperage to fully function the tail lights.

Aside from that I would recommend starting at the trailer connector on your vehicle checking for corrosion or exposed wire and trace the wires back checking for damage and fix as necessary.

You could also try using a better ground for the right light assembly. It could be that the ground is not quite strong enough to work with your vehicle wiring so it does not function properly.

I attached an FAQ article on trailer wiring for you to check out also.

expert reply by: Jameson C