How To Wire The Optronics Transit Tail Light # ST90RB

Updated 11/06/2024 | Published 10/29/2024

Products Featured in This Question

Optronics Transit Tail Light - Brake and Tail Light - Incandescent - Surface Mount - Round - Red

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$35.23

Digital Multimeter with 42" Long Test Leads - LED Display

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$22.52

Question:

My pervious Bergman vintage lights had a metal backing which touch the aluminum of the camper and helped with the ground. These new ones have no metal. How do I ground them? The light is super light when connected. My photos are not uploaded

asked by: Kirsten N

Tail light
(click to enlarge)

Expert Reply:

Hi Kirsten,

The Optronics Transit Tail Light # ST90RB has a power and ground wire and would need to either be grounded to the frame using a ring terminal and self-tapping screw or tied into a ground that's already in place. In the picture it looks like you already have two wires that you're spliced into. Did you confirm what the functions of those wires were prior to connecting the light?

Brown is typically your running light wire and green can be used for ground quite a bit so I'm wondering if you potentially just have this hooked up backwards. I would connect your tow vehicle to the trailer and then turn on the running lights and test both wires with a multimeter # PT89ZR to see which has power and which doesn't.

expert reply by: Kevin C

Kirsten

11/4/2024

Btw, I tried the wires both ways with the same results. The ground wire goes to the frame in the front near the hitch. Is it possible that is not enough and I need to ground to the aluminum skin? Since the old light had a metal backing it seems it might have had extra grounding? I purchased the multimeter you suggested but am thinking the lights are a problem, since the old lights worked previously.

Kevin C.

11/4/2024

@Kirsten Aluminum is not a good conductor so tying into aluminum only would not give you a strong enough ground. The previous lights probably had a steel band on the back of them that they were grounding to. Does your trailer have a junction box with the ground for the lights connected to the ground from the 7-way cable or is it just grounded to the frame?

Kirsten N.

11/4/2024

@KevinC The previous lights had a stainless steel backing that touched the aluminum skin. There is no junction box. The 7 pin goes straight to the lights

Kevin C.

11/5/2024

@KirstenN There would be a junction box on your trailer. It would cost too much money for the manufacturer to run that high of a wire gauge all the way from the 7-way to the back of the trailer. If you look at the frame around the tongue and possibly even right under the trailer body at the front there should be some sort of box, plastic or metal, that all your trailer wiring runs to. Most trailer manufacturers just use a cheap 4x4 metal junction box. In this box will be the ground for your 7-way cable. The lights can be tied into the 7-way ground which is grounded through your tow vehicle.