How Does the Optronics Trailer Light # STL79RB Wire to Trailer Wiring

Updated 09/10/2025 | Published 03/26/2013

Question:

1. white, 2.. yellow/green and 3. brown 4. RED left Black right How do i wire the RED BLACK?

asked by: Rand C

Expert Reply:

The wiring of the Optronics Trailer Light # STL79RB that you listed are:

The white wire, with the mounting eye, is a ground wire that needs to be connected to the white wire of your trailer wiring.

The black wire would be connected to your running lights and is the lower intensity illumination. This should be run to the brown wire of your trailer wiring as this is usually the tail light circuit.

The red will be wired to the brake/turn wire and is for the higher intensity illumination. This will get run to either the yellow or green wire depending on which side of the trailer you are on. The green wire should be on the right side of the trailer and the yellow will be on the left side.

If this does not work the best recommendation I can give you would be to test the circuits on your trailer with a circuit tester like our part # 3808 to determine the functions of the wires on your trailer and wire them accordingly to the # STL79RB.

You may find that the extra wire you have on your trailer wiring is a reverse light.

I attached an FAQ article on trailer wiring for you to check out also.

expert reply by: Jameson C

Rand

3/29/2013

thanx... electric is either plus or minus- so simple .. and sparks when its wrong..

Kurt

9/10/2025

Regarding the red wire: if connected to green (right turn signal) or yellow (left), I understand the higher intensity will illuminate when the brakes come on, but depending on which wire you connect to, won't the unit also flash with the particular turn signal? My current Optronics Light Strip, stock on my 2006 Heritage trailer (SeaRay SunDancer) which I need to replace looks identical but has four wires (and half the diodes flash on either side along with the respective turn signal, which seems to be a function that is no longer available?).

Jameson C.

9/10/2025

@Kurt yes this is true. To get an isolated brake signal you would need a # C56196 as the circuits are combined.

Kurt

9/10/2025

@JamesonC Thanks for your prompt reply, Jameson. I think I need a didactic session explaining why this evolution in wiring has taken place. It feels like we're going backwards. As an aside, in talking to Optronics today, it may be that my original 4 wire unit is the STL80RB which is out of production.

Jameson C.

9/10/2025

@Kurt in recent years they trailer components have attempted to get a little more standardized in some ways and one of them was with lighting and wiring. That is why you don't see as many dedicated third brake lights anymore on trailers. You can still add them with a signal converter but many people just go without.