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Troubleshooting Side Marker Lights on 1999 Dodge 3500 Diesel Dually


The running lights in the headlights and tail lights work fine. The triple lites on the roof of the cab work fine. The running lights on the SIDES OF THE BED dont work, I tested them and both leads + and - are shorted to ground. One 5 amp fuse in the fuse panel has low voltage, test light lights up dimly. Very weird. I do have a trailer connector on the truck but nothing plugged into it at the moment. Any ideas?


Expert Reply:

First I suggest you check the wiring for the affected lights looking for a loose ground wire (or loose mounting post if the light uses the post for ground) or for any wiring that has visible damage. Check for wear spots or cracks in the insulation and repair or replace damaged wire as needed. Make sure the grounding points are clean and free of rust, grease, primer and paint.

Next make sure the main wiring harness ground is solidly attached to a clean spot on the vehicle. This too needs to be solidly attached to a clean bare metal surface on the vehicle frame. It is fairly common for a weak ground to make itself known only when running lights (which pull more power than turn lights because they remain on continuously) are activated. Other lights can still work with a weak ground even if running lights do not.

You can also check the fuse panel to ensure the contacts for the circuit's fuse are not corroded and that the appropriate value fuse is installed.

If you prefer to replace the 4-pole harness you can use part # 118329 which plugs in at your taillights.

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