Rear running lights not working

In answer to dittmer, in some cases, such as on my 2008 Tioga, which has plastic molding on the top and sides of the rear cap, pulling back on those moldings often times reveal how they ran the wires to the lights. My top molding has all the wires to the side markers, while the vertical molding has the wires to the rear lights. If yours have those moldings, try pulling them back about an inch an a half. Also, my previous suggestion of using a ground wire was merely a test to see if it was a ground issue or a power problem, and once the problem is determined, running new wiring is entirely a different matter.

cgmartine wrote:
The most simple and easiest way to check it is to run a temporary ground wire from the nearest grounded point to the ground point on the inoperative light. If it works, then you automatically know it is a ground issue. The solution in that case is to run a whole new ground wire. If providing a solid ground wire does not fix the problem, then you have no dc power, and will need to supply it, preferably from a good known source.

Good advise for when you can get the wires to the lights. Unfortunately those high mounted lights are generally very difficult to re-wire. Hopefully the trouble can be found below.

Given the rear high mounted marker lights work as parking lights, the wires most surely will be routed from top to bottom inside the back wall and connected down below under the RV, pending the rig catching a rear tail light along the way. Given how and when Kathy's lighting issues surfaced, I would think her answer will be found underneath the rig near the rear bumper.

Of coarse I could be wrong, but that is the best place to start debugging.

The most simple and easiest way to check it is to run a temporary ground wire from the nearest grounded point to the ground point on the inoperative light. If it works, then you automatically know it is a ground issue. The solution in that case is to run a whole new ground wire. If providing a solid ground wire does not fix the problem, then you have no dc power, and will need to supply it, preferably from a good known source.

I'd suspect a short circuit, perhaps from the newly installed trailer plug, resulted in a fuse blowing. That happened to me many years ago, with my MH pulling a boat. There was a short somewhere in the trailer wiring that blew a fuse in the MH.

Look for a poor/disconnected ground connection from the tail light assembly to RV frame.

I am not familiar with your particular rig, but motor homes in-general, all lights attached to the house portion of the rig are often sub-standard compared to the original chassis wiring. RV manufactures often use non-sealed crimped connections which are very susceptible to water and salt infiltration and also if not crimped correctly, will come apart or have intermittent contact.

I suggest you get under the rear of your rig and visually look for an unconnected hanging wire. If all appears to be okay, have your spouse or friend look at the marker lights while you gently shake the wires. If you get intermittent action, then you know where the trouble is.

ADDING: The comments added just below are also good tips, checking fuses, shorts, and ground wires. Ground wires are often green with an eyelet on the end, attached to the steel chassis frame with a screw. If it is rusty, it may need to be cleaned to work proper again. Once cleaned with steel wool, add a blob of grease to help protect it. I personally like to use clear silicone grease to seal and protect all such terminations. Anything crimped, I like to solder and use shrink tubing for best reliability. But most people don't get that particular.

For clarity, the upper tubular pieces pictured are crimped connections, the lower ones are eyelets, also crimped. The yellow, blue, and red colors determine the diameter wire to use it with.

Have you checked the running light output from the plug with a volt meter? May be a bad connection on the RV side of plug.