How to Use a Taillight for Both Third Brake and Running Light Functions

Updated 06/22/2024 | Published 11/03/2017

Products Featured in This Question

Thinline LED Trailer Tail Light - Stop, Tail, Turn - Submersible - 9 Diodes - Red Lens

(1471)

$15.84

2-to-3 Tail Light Converter for Towed Vehicles w/ Incandescent Tail Lights

(172)

$38.79

Deka Heat Shrink Butt Connector - 22-18 Gauge - Nylon Insulation - Red - Qty 5

(1104)

$5.11

Question:

I would like the third brake light to also have the running light tail light function. So could I add the converter for the brake light and then just run the brown tail light wire to the brake/tail light? Thank you!

asked by: Jack

Expert Reply:

In order to use a third brake light for both brake and running light signals, you would need to use a light with turn, brake, and running light capabilities such as the Thinline LED Trailer Tail Light part # STL59RB. As most trailers are a 3 wire system you would also need to use the Vehicle to Vehicle Tail Light Converter part # 118158 to separate the brake signals from turn the signals.

In order to install the light you would first need to take the ground wire (white) from the taillight and attach it to a clean bare metal surface. You would then take the brake light wire (black) from the taillight and connect it directly to the running light wire (brown) on the trailer. Finally, the turn signal light wire (red) from the taillight will need to be attached to the red wire on the converter box. The other two yellow and green wires on the output side of the convert box will not be used. I also recommend using the Deka Heat Shrink Butt Connectors part # DW05743-5 to make these connections.

I have attached a review video of both the light and converter box for you as well.

expert reply by: Conner L

Ryan

6/21/2024

So ,2019 ram has trailer connector in bed. I added topper to truck. Wanted to add power for brake light,also power to dome light Possibly utilizing 7 pin 78119 connector! Which I have. The third brake light ,and dome light have a male 3 pin flat connector already on the wires I would appreciate guidance.

Bryce D.

6/22/2024

@Ryan Hey Ryan, so basically all you'd need to use is the 3rd Brake Light Logic Module # PP20-702 and the Pollak # PK12706, and and then some loose wire and connectors to attach it all together. The Reese 78119 connector isn't going to work for this, unfortunately. The logic module will feed into the right or left stop/turn pin on the connector and then you run the output to the third brake light. It will also need to be grounded as with the connector but the other slots will remain blank.

Ryan

6/22/2024

@BryceD so if I splice into light as per usual I don't need pp20702 or pk12706! So that would give brake correct? Then all I need is power? Can I pull power off of seven pin receptacle by splice at receptacle? Or should I run all the way to front and pull from battery?

Bryce D.

6/22/2024

@Ryan You're going to need both the third brake light module as well as the Pollak connector. The Pollack connector would just get plugged into your in-bed 7-way and provide the power.