Faulty Left Directional and Brake Lamp on Trailer Towed by 2004 Toyota Sienna

Question:

2004 Sienna lights all function properly. Boat trailer lights work on right side. Left side light works, but brake and turn signal do not. Checked yellow wire but found nothing. HELP

asked by: phil

Expert Reply:

In order to diagnose the problem, you will first want to test the trailer connector on the Sienna. Use a circuit tester like part # PTW2993. Check the socket that corresponds with the yellow wire which carries the driver's side brake and directional signal. If you get a signal at this location with both functions activated, the problem exists somewhere on the trailer. Start at the connector on the trailer, inspect it for damage or corrosion and replace or clean if necessary. Trace that yellow wire all the way back to the lamp, checking for broken or loose wires or connections. Look for spots where the wire might be pinched, or spots where the wire insulation might have rubbed off. Make sure the connections at the lamp are secure.

If you do not get a signal at the connector on the Sienna, trace the wires back until you locate the converter box. While a helper activates the left turn signal, test the yellow wire on the input side of the converter, and then at the output side. If you have a signal going into but not out of the box, the converter is bad and should be replaced. If you should find that the converter needs replacing, use part # 118304.

expert reply by: Mike L