Locating and Fixing Running Lamp Problem on Trailer Towed by 2004 Dodge Ram

Question:

All my light work on my trailers except my running tail lights iv checked plug and ground what eals could it be

asked by: Jeff

Helpful Expert Reply:

Is this occurring with more than one trailer when used on the same vehicle? If so, the problem is on the vehicle. If it's happening with only one trailer, you'll want to use a circuit tester on the trailer connector at the pin in the 11:00 position while the truck's headlights are switched on. We offer a circuit tester as part # PTW2993 if you need one. If you have power at that pin, the problem is somewhere on the trailer in the running lamp circuit between that pin and the lamps.

Take a look at the corresponding pin on the connector on the trailer. Is that particular socket damaged or corroded? Repair or replace as needed. Trace that running light circuit from the lamps back up to where it connects to the trailer connector. Look for broken connections or loose wires. Many trailer lamps don't have a separate ground wire, they will ground through the fastener connecting the lamp to the trailer. If this mount is corroded, you won't get a completed circuit.

If you are NOT getting power at that pin on the trailer connector, you likely have a blown fuse. For the 2004 model year, the Dodge Ram owner's manual wasn't terribly specific regarding which fuse location protects the trailer running lamp circuit, but according to the forums it looks like the 20A fuse in location # 15 is the one you're looking for. The lid of the fuse box in the engine compartment should have a diagram showing the fuse locations either on the top or the underside. Replace the fuse with an identical 20A fuse.

Keep in mind, replacing the fuse if it's blown is only half the battle. If it IS a blown fuse, you'll need to locate and repair the short before plugging the trailer back in, or you'll continue to blow fuses. As mentioned above, you'll want to trace that running lamp circuit, looking for pinched or broken wires, loose connections and cracked or worn wire insulation. Any point where a wire passes through a hole in the frame is a likely spot to check.

I've linked you to a trailer wiring troubleshooting article that you might find helpful.

expert reply by: Mike L