Using A Marker Light With Two Wires To Replace Old Light That Only Had One Wire

Updated 07/13/2026 | Published 06/08/2022

Question:

Im replacing old trailer marker lights the ones on the side with new ones. The old ones just had one wire, black. The new ones have both red and black. Which one do I hook up? What do I do with the other one?

asked by: Janet R

Expert Reply:

Since your old trailer light only utilized one wire that means the one wire was used for power and the old light got it's ground through the mounting hardware.

Since the new light like # MCL44AB has two wires, one for power and one for ground, you'll just need to connect the black wire for power to your trailer, and then run the white wire to your frame and ground it.

expert reply by: Bryce D

Sabrina

7/13/2026

What if your trailer is aluminum? Do you still connect the ground to the trailer?

Robin H.

7/13/2026

@Sabrina you can try it but typically there is a ground wire running back to the lights. I would check for that and then you can run a jumper to it.