Troubleshooting Trailer Left Turn/Brake Lamp Circuit on 2018 Ram 3500

Question:

I have a 2018 ram 3500 I’ve checked all my fuses and trailer has been checked my truck side has a issue the left turn and brake won’t work on trailer we hooked trailer to other truck lights work fine any suggestions? I was told it may need to be flashed

asked by: Dewayne P

Expert Reply:

If you've recently added a trailer connector, it's completely probable that you'd need to have the truck reflashed at the dealer. This is a fairly common occurrence with FCA vehicles.

Have you checked the pin in the 9:00 position in the 7-way trailer connector with a circuit tester like # PTW2993? With the turn signal on, the tester should blink when that pin is touched. If you're not showing signal on that pin, unplug the connector from the rear of that trailer connector, and probe the sockets in the trucks harness. If one of the sockets in the truck harness makes the tester blink along with the turn signal, then the 7-way is faulty and should be replaced with a new one like # HM40975.

It you're not getting any signal on the vehicle harness, you either have a blown fuse or a wiring fault. The fuse for the left trailer turn/stop lamp is a 20A fuse is in position F53 in the engine compartment fuse box. Sometimes it's difficult to visually tell if a fuse is popped, so try taking the right turn/brake lamp out of position F81, and see if that fixes the problem. If it does, then simply replace the bad fuse. If that does't fix the issue, then you have a wiring problem somewhere between the fuse box and the trailer connector that you'll be best off having the dealer hunt down.

expert reply by: Mike L