bing tracking image
Q & A Icon

Solution to Allow Trailer Running Light Circuit to Function on 2019 GMC Sierra 1500


my trailer running lights dont work but brake and signal do. I tested truck plug with volt meter, no power running light pin. Fuse is good. brought it to dealer he said system is pulse width modulated and he had to connect a bulb that draws more than 55ma to test power at pin and it worked said I need a load resisters series to get lights to work. took truck to trailer guy, he tested truck plug and said it was good. I went home connected old headlight bulb to old 7 pin cord only connecting to running light pin and ground. turned headlights on and it worked. tried connecting trailer again and found lights went on for 1 sec so I turned lights off then back on and running lights went on for 1 sec again, every time I turn headlight switch off then on lights will go on for only 1 sec then nothing. maybe I need the load resister but doesnt make sense


Expert Reply:

The trailer wiring on the newer trucks like what you are experiencing on your 2019 GMC Sierra 1500 and the new Ford trucks with the "smart tow" package are proving to be challenging for reasons like what you found where the truck doesn't want to show a trailer connection.

The easiest solution you'll have will be the 7-Way Trailer Adapter # C57003 which was designed for German vehicles towing trailers with LED taillights that has load resistors built into it. Basically you'd install this adapter into your current 7-way, your trailer into the socket, and then you'd have load resistors on the circuits which will allow them to function.

expert reply by:
Jameson C

Products Referenced in This Question

Product Page this Question was Asked From

Q & A Icon

Similar Expert Q&A Pages

See More Q&A Expert Answers >>