Troubleshooting Trailer Wiring With 2002 GMC Sierra 1500HD

Published 01/25/2018

Question:

I have a curt installed already. Problem I have is all signals work on both 7 and 4 position connectors using a meter and connected to my LED single car auto-transport trailer. I have a old bulb trailer that using a 12v battery all lights work. But if I connect bulb trailer to truck no bulb lights work. I tried jumping a bulb across LT/brake to ground on truck and bulb light doesn't work, no voltage. Bulb trailer has worked for over a year, acts like curt can't supply current?

asked by: Jeff

Expert Reply:

There are taillight converters available and it is possible I can find something to work for you though I would need to know the year of your GMC Sierra 1500 in order to find out. If you can get back to me with that information I can try and find a solution for you.

expert reply by: Kyle S

Jeff

1/25/2018

Kyle S.

1/25/2018

From your description, since the lights work on your trailer with LED lights but not older, incandescent lights it sounds like there may be a short in the wiring which is causing the issue; a harness should be able to supply enough current to your lights. The lights work when connected using a 12V battery but that could be enough direct current to circumvent a short so that is going to be the first thing you'll want to look for. If you have not already you are going to want to test the connector on that trailer as well. Another issue you will want to take a look at are the ground connections, as they can be the cause of numerous lighting problems. You'll want to make sure your grounds are securely attached to bare metal surfaces free of any paint, dirt or corrosion of any kind. Also check your wiring thoroughly to ensure there are none that are crimped, broken or otherwise damaged. If possible, check and see what amperage your Curt harness is rated for because it is possible that you are overdrawing. You can also remove some of the incandescent bulbs and see if it works after that, which would also indicate an overdraw. I've added links to a pair of help articles on trailer wiring that you may also find useful and if you cannot find the issue after doing this troubleshooting let me know and we can continue to work on the issue.