Only 2 Diodes Light Up on 10 Diode LED Lights

Question:

I changed the taillights on my older utility trailer to 6inch oval 10 diode LED lights. When first checking, only the top and bottom diode lit and they were weak. I cleaned up all the grounds and rechecked. I still only have the top and bottom diodes on both lights but they are stronger. Why are not all of the diodes lighting up?

asked by: Paul

Expert Reply:

Checking all of the grounds like you have already done is the first step, including the main ground on the trailer and the vehicle's trailer connector ground. It is a good idea to check all of the trailer wiring for any damaged or frayed wiring because there may be a short in the wiring. I would ground the taillights to a trailer battery and touch the wires to the positive post to see if each light illuminates properly. You also want to make sure the connector on the trailer side and vehicle side is free of corrosion or bent pins. Also check that they are seated together properly.

If the functions on the lights illuminate properly then you know the issue is not with the lights themselves. If you test for function and the lights do not properly illuminate, then the taillights may be defective. It also could be related to your tow vehicle's wiring. You want to test the functions of the trailer wiring on the vehicle for power using a circuit tester like part # PTW2993. Specifically check the running light circuit on the vehicle's trailer connector for power. If you are getting power to the circuits on the vehicle's wiring, then you know that the issue is on the trailer side. If you check the functions on the vehicle wiring, you do not get power then you may need to replace your trailer connector.

expert reply by: Heather A