Troubleshooting 3 Malfunctioning Trailer Marker Lights # MC53RB on 2007 PJ Flat Bed Trailer

Question:

2007 PJ flat bed trailer, 2000 pound. Three MC53RB red mounted in the center rear frame. Is this a series circuit one light burns out, they all go out? Or a parallel circuit one light burns out, the other two remain lit? Right now all three are out. All other lights on the trailer are working property. Thanks.

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Helpful Expert Reply:

The Optronics Round 2-Inch Sealed Flush Mount Trailer Clearance Light you referenced, part # MC53RB, can be installed either parallel- or series-wired. I was not able to find wiring information on the PJ Trailer website. Please note this incandescent light assembly is factory-sealed and does not have a user-replaceable bulb.

The malfunction with all three of these lights could result from one of them failing in a series-wired configuration, from a bad ground, or it could result from a problem in the trailer wiring itself. If all failed at one time this suggests either a series wiring arrangement (and at least one damaged light) or a common issue with the wiring that serves all three lights.

Please refer to the linked diagram of a common trailer wiring configuration. If your right and left rear tail lights are still working (the lights indicated by the yellow arrows) then I would start off by examining the wiring to the clearance lights.

Check for loose or corroded plugs and wire that has wear spots or cracks in the insulation. Pay particular attention to points where the wiring may touch the trailer frame. Repair or replace any damaged wiring. Make sure the ground wire that connects these lights to the trailer frame is secured to a clean bare metal surface. Clean the grounding point(s) if rusty or relocate the ground lead to a new clean spot on the trailer frame. If you find that you need new plugs you can use part # A86PB or # A46PB.

If you have a spare battery on hand you can troubleshoot each individual light unit by applying 12V power one at a time directly to the two input terminals. This is the best way to eliminate the lights themselves as the problem. If each light works when tested on its own then you know the issue is somewhere in your wiring. If any of the individual light units does not function when tested in this manner you can try bypassing it to see if the other two lights work. If this is the case then you know you need to replace the one light.

If your trailer has a tilting bed, then the pivot point may not provide an adequate ground connection. The solution to this issue is to route a ground wire from the connector at the front of the trailer to each lamp assembly at the back of the trailer bypassing this pivot point.

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helpful expert reply by:
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Adam R

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