Troubleshooting Trailer Running Lights Not Working

Question:

I have upgraded all running lights and tail lights to LED on travel trailer. Clearance lights work, signals work, brake lights work. What does not light up are the running light portion of my 1157 bulbs. This bulb functions are running, turn signal and brake. I have a separate 1156 bulb that is backup function that works fine. The running function of the 1157 does not light. It is getting 12 volts and grounding is good. It works with an incandescent 1157, but not an LED 1157. I have tried a resister 6 ohm 50 watt on each 1157 LED with no luck. The resister gets hot, but bulb does not light. What am i missing? This is the case for 2 vehicles that pull this trailer, so i assume its at the trailers end. Thank you!

asked by: John

Helpful Expert Reply:

There are a number of potential issues that could be causing your running lights not to work, but you will have to troubleshoot the problem with some detail.

The first thing to do is take a look at your vehicle's owner's manual to locate any trailer fuses or relays and ensure they are all there and in working order. If they are, in order to determine the specific problem you will need to purchase a circuit tester if you do not have one - the very handy Cordless Circuit Tester # PTW2979 would be my strong recommendation due to how easy it is to use - and test the connector on your vehicle after disconnecting it from your trailer. Check the wiring going into your harness from your tail lights to see if those wires are carrying the correct signals, if not then the issue is with the vehicle wiring.

If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring. You will also want to check both your vehicle and trailer connectors for corrosion, which can be green or white in color. A build-up of corrosion can interfere with the signals getting through the connectors so if it is present you are going to need to either replace the plug or clean the corrosion. Even though you said your grounds are good, we always recommend double-checking to make sure your grounds are attached to bare metal surfaces and free of any paint, dirt or corrosion.

I have added links to a pair of help articles on trailer wiring, including a troubleshooting guide which I highly recommend taking a look at.

expert reply by: Kyle S

John

9/18/2019

Kyle S.

9/18/2019

I'm a little confused by what you are saying because you mention "clearance lights work" but say the running lights do not, though those are the same thing. I was unable to find your order number to see what you purchased from us, just replacement bulbs or new lights altogether. My thinking is you purchased just replacement bulbs and the issue may be that the bulbs simply aren't compatible. This is really the only thing that makes sense if everything else is fine and the power and ground are good. For that reason, I highly recommend purchasing stand-alone LED running lights to resolve the issue, such as the Optronics LED Trailer Clearance or Side Marker Light # MCL95RB (Red) or # MCL95AB (Amber). I have added links to video reviews and an install of these lights as well as a link to our entire selection of LED lights for you to take a look at.