Forum Discussion

CJW8's avatar
CJW8
Explorer
Oct 30, 2014

Clearance lights not working.

I have a 2005 Forestriver 5th wheel toyhauler. When I unhooked the last time and pulled away the trailer plug (7 pin) got caught on the tailgate and pulled put of the junction box of the trailer.

The #10 positive that runs to the batteries shorted and melted a lot of it's own insulation. All would have been fine if Forestriver would have landed the wire on the correct side of the circuit breaker.

I replaced the 7 pin plug and cable with a factory made one. Everything works except the clearance lights on the trailer.

Since the wires from the junction box on the pin box are hidden in the 5th wheel overhang with no access, I couldn't access the damage from the shorted wire. My solution was to bypass them all with a new 7 wire cable and splice it in inside the propane compartment where all of the wires are accessible.

I cannot find the power and ground going to the clearance lights. is it possible it is located in the 5th wheel overhang?

Any thoughts would be helpful. Thanks.

8 Replies

Sort By
  • CJW8's avatar
    CJW8
    Explorer
    Oct 31, 2014
    YES! That did it! Thanks Forest River for making a hidden connection! Now, since I can't see to inspect those hidden wires and it is possible that the hot wire that melted could have compromised the insulation on other wires, I am going to install an inline 15 amp fuse in the POS for the clearance lights just in case.

    Thanks MEX for making me think about the cut out wires.

    It was not a wasted effort because I cleaned up all of my tail light wiring eliminating factory crimp nuts and installing waterproof butt splices and refreshing the grounds with new screw to frame and waterproof ring terminals.

    Another success story.
  • CJW8's avatar
    CJW8
    Explorer
    Oct 31, 2014
    MEX,
    All wires are that were cut out are connected at both ends. All functions have been tested by plugging into vehicle. A second test was done by jumpering black (pos) on the trailer plug to each light function and all worked except clearance lights which should have come on with the tail lights. What I can't see are the wires from cut end to cut end because they are hidden in the overhang and will not pull out, must be clamped in there. Maybe the power for the clearance lights are spliced on in the overhang and that is why I cant find them. Next test it to apply power to king pin cut end green and white and see if they come on.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Oct 30, 2014
    On the part that was ruined and cut out, are there unidentifiable wires? Insulation color codes? Have you audited all wires on the trailer side and can account for all functions?
  • BFL13's avatar
    BFL13
    Explorer II
    Oct 30, 2014
    Can you do Mex's trick and just apply the pos alligator clip to the lamp's positive? If the lamp's ground is good then the lights should still go on?

    Not sure how it would apply and I'm sure the OP knows this, but on ours, in daylight, the headlights don't come on just the truck's day running lights (which may not apply to American vehicles--I am not up to date on that) So to turn on the trailer's clearance lights in the daytime you have to switch the truck lights from "auto" to headlights.
  • CJW8's avatar
    CJW8
    Explorer
    Oct 30, 2014
    MEXICOWANDERER
    I already did just as you suggested and all the clearance lights came on but not the tail lights. While it was hooked up as you suggested I checked for voltage on the abandon wires in the overhang and there was none.

    BFL13
    There is only a circuit breaker in the kingpin junction box and it is on the battery line. If there is another fuse box somewhere else, I have never seen it.

    I will keep looking.
  • BFL13's avatar
    BFL13
    Explorer II
    Oct 30, 2014
    There was a thread a while ago where ISTR it turned out the guy's rig had the clearance lights at the back grounded from one of his tail lights (licence plate?) lower down which was grounded somewhere. So the pos wires to the lights are one thing and the neg wires another.

    Here is how ours are. The "running lights" are with the licence plate light. In ours the kingpin junction box is also a fuse holder and there is a cable hatch access door up under there where the 7-pin cord comes out from.

  • JaxDad's avatar
    JaxDad
    Explorer III
    Oct 30, 2014
    Before you get too crazy trying to trace wires, check that the 'trailer only' fuses in the second fuse box under the hood are all ok.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Oct 30, 2014
    I would first check to see if the circuit was valid.

    Remove lens and bulb on one lamp. Jumper two wires from your open tow vehicle hood and use that vehicle battery for test. Alligator clips help. All the rest of the clearance lights should light up with no major sparks. The color of the pigtail connection (you have to remove the lamp base to see this, will tell you the color of the wire to look for in your 5th wheel overhang. At the time of the looksee of the loose lamp verify the lamp negative is not made through the chassis of the trailer.

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,240 PostsLatest Activity: Apr 26, 2025