How To Wire a Trailer Tail Light with Yellow, Black, Red, and White Wires

Updated 02/09/2026 | Published 04/29/2019

Products Featured in This Question

16 Gauge, 4 Conductor Bonded Parallel Wire - Per Foot

(237)

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Fusion LED Combination Tail Light Bar for Trailers Over 80" Wide - Submersible - Red/Clear Lens

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$26.94

Question:

I have taillights that have 4 wires blk red yellow and white. What is each color

asked by: William

Expert Reply:

The best way to find out what each wire is for on your tail light is to take a 12 volt power supply and apply that to each of the wires to see which bulb it illuminates. I cannot really give you an exact function for each color as it could vary from manufacturer to manufacturer.

With that being said, we have the Fusion LED Combination Tail Light Bar part # STL264RB which contains white, black, red, and yellow wires. The functions of these colors on this lights are as follows. This may be similar to what you have but it will be best to test with 12 volt power before making your connections.

Black: Tail
White: Ground
Red: Step/Turn
Yellow: Backup

expert reply by: Conner L

Robert

2/7/2026

I have a 4 wire trailer light Black White Red Yellow My trailer wires are Brown Green Yellow White Witch wire goes where

Robin H.

2/9/2026

@Robert without more information on the light itself I can't say for sure. The trailer wires are likely the standard, brown is running lights, green is right turn/stop, yellow is left turn/stop, and white is ground. White is probably power on that light, yellow I would try matching with yellow and then you can connect and test the others to see what the functions are. It won't hurt the light if you wire it incorrectly so if you don't have a wiring diagram or other information on the light trial and error is your best bet.