red and yellow marker lights not working at all

[MfgWorry]

Need help finding problem why outside marker lights are not coming on. there is power at the plug, but none to the marker lights outside the unit. brake lights all work fine. Is there a breaker or something in the 5th wheel that controls the outside marker lights. My dealer said mice or rats may have chewed the wires and caused a short somewhere...but where, I have not idea of where the wires go to the marker lights or what color the wire is for the marker lights. Got any ideas on what to do.

[tim_and_amy]

You can jumper Pin 4 across to Pin 3 on your trailer side plug. Your coach battery will turn on the Running lights on your trailer. If this works then you know it is an issue from the truck running light plug. If they do not turn on, then you need to go to the rear of the trailer and check to see if you have running lights at the tail lights.
In some applications, the MFG will run the solid brown wire to the trailer tail lights, the side marker lights will be Tee Tapped off of the brown wire, but daisy chained together in parallel.
If your tail lights are on, but the side markers are off, then it is the connection point at where the side markers attach to the brown wire.

If the tails and Side markers are out then do the following.

Remove the jumper for testing I mentioned above.
Using a Digital Multi Meter, put on DC volt.
Place the red lead into pin 4 (battery voltage) and black lead on pin 3 (tail lights), Do you see voltage across these two pins?
Yes, ground is good and voltage is flowing, check bulbs and grounds at each point.
No,= Ground or power not working, Confirm as follows.
Remove the black lead and touch to Pin 1 (ground) or touch non painted surface on trailer hitch or trailer frame. Do you have power?
Yes, Ok, battery is OK and so is power to plug.

Verify if Tail Light Harness is good or has broken connection.

Remove red and black lead from trailer side of harness.
Place meter on continuity
Put Red lead into Pin 3 of trailer side of harness.
Touch Black lead to either Pin 1 (Ground) or to trailer frame. (must be paint free area).
Does meter BEEP? Or indicate that there is continuity to ground?
Yes, connections from plug through entire harness may be OK, unless shorted to ground. Must remove all bulbs and retest.
With all bulbs removed, does it indicate continuity to ground? (Beep)
Yes, =Bad, means short of power feed to ground. Wiring or socket connectors need inspected.
No= Good, means no short to ground, install bulbs
Re-check, with all bulbs back in, is there continuity to ground?
Yes, ok Wire harness and bulbs are all good,
Issue is on truck side.
On truck side, turn on running lights, does truck lights work?
Yes,= test truck side connector. Using DVM or harness tester, go from pin 3 truck side harness with red lead and black lead on either Pin 1 or touch metal on truck frame, bumper or receiver bare metal spot.
Does it indicate power?
Yes, hmmm, this will get complicated,
Must now connect trailer harness and remove one of the side marker light covers then check for power. If lights are not on then there is no power obviously, but might be loss of ground between trailer Pin 1 and truck Pin 1.
Remove bulb from side marker light or tail light, put red dvm lead on pin at bulb socket that is the power side of the pin, and black lead to chassis ground or trailer frame, you could use a long piece of speaker wire or such, to wrap around the black lead and touch the truck receiver, is 12vdc showing?
If yes, then it is a flaw in the ground between the truck and trailer.
FYI, you could also, test, as long as ONLY the trailer harness is connected, on continuity, go from coach battery Ground, with red lead, and touch the black lead to the trucks receiver hitch and see if you have continuity from the battery, through the harness, to the truck frame. If yes, then ground is OK between truck and trailer.

If you find you don't have power at the trucks side of Pin 3 then you need to look in your owners manual to see if you have a separate tail light fuse, FYI, many newer vehicles do have a separate trailer harness fuse.

[RoyB]

I have one of these testers in my RV tool box that connects to the truck side to tell if all is OK with the truck side. This helps when troubleshooting...

I got mine from AMAZON but have seen them at local auto parts places - also at ETRAILER.com



This is also a general schematic of how a typical trailer is setup using the 7-way trailer wiring connector. Good reading at ETRAILER.COM on how all of this is setup.




I always squirt WD40 in the trailer connector and move around several times before hooking to make sure the pins are making good connect.

You are going to have to start tracing out the wires if you don't find anything inside the marker lights... All of this wiring is controlled by the truck. Does not interconnect with any of the trailer 120VAC or 12VDC wiring except for connection to the trailer battery.

Roy Ken

[jaycocamprs]

Find the box where the pigtale ends. If all running lights including the tail lights quit at once this is the most likely place. Likely a brown wire.

[Bull_Rider]

What does "power at the plug" mean? Are you using a meter and your checking the running lights, tail lights feed on the vehicle side at the connector?

There's a way to use a spade type fuse to jump across the trailer connector to illuminate the RV running lights. Every now and then someone will ask how to turn on the running lights while unhitched. If you could find one of those posts and follow the instructions it would help to find out where the problem lies.

I just had this problem and found a blown 15 amp fuse for the RV tail lamps on the truck.

[kroghville]

Ralph, I recommend you take a 12 volt tester and see if you have power at the fixture before you go through the work of cleaning all the fixtures. If you have power, then by all means make sure the fixture contact areas are clean. A small shot of WD-40 would be appropriate at this time. If all of your lights quit working,I suspect a fuse,wiring, or connector problem.

[midnightsadie]

mr duck is right,also take the screw out at the light fixture and clean ,and remember to do this with the plug unhooked or you could blow the fuse. this is a good case where the light fixture is dirty and not geting a good ground.

[Roman_Duck]

Corrosion inside of the marker lamp is a good cause. Start by removing the lens covers from your marker lamps. Clean light contacts where the bulbs connects to fixture. Quite often the lights get oxidation occurring from lack of use, Most people travel during daylight hrs. and the marker lamps get used less than the tail lights