What is the Function of the 5th Pin on a Trailer Connector 5-Way Flat Connector

Updated 02/24/2026 | Published 05/06/2016

Question:

what is the 5th pin on the 5 way plug? I have a trailer with surge brakes and that pin needs to disable the brakes when backing up.

asked by: Troy

Expert Reply:

The 5th wire on a 5-Way flat connector is intended to connect to the vehicle's reverse light circuit. This is for the exact situation you described, so the 5th wire can signal a surge coupler's electric reverse lockout.

If you need a 5-Way flat trailer-side connector, you can use the Draw-Tite 5-Flat Trailer End 48 Inch Harness # 20017. This connector is designed for the 5th wire to carry the reverse light signal from the vehicle to the brake actuator.

The # 20017 connector will work well if you have a 5-Way flat vehicle side connector on your tow vehicle. If you have a 7-Way round, blade-style connector, an adapter like the Optronics Adapter 7 Pole to 5 Pole Flat # A75TB.

If you have a different wiring set-up on your tow vehicle and need to make it compatible with the 5-Way flat wiring on the trailer, feel free to tell me more about your tow vehicle set-up and I will be happy to make a more specific recommendation.

expert reply by: Victoria B

Drew

5/14/2020

I have a similar situation. On my truck, I have a 4 pin flat connector and I need either a 5 pin or a 7 pin. Whichever actuates the reverse lockout.

Chris R.

5/18/2020

On your truck you can simply add an adapter like the Tow Ready # 20036. This will plug right into your existing 4-Way to provide you with a 5-Way connector at the other end. The additional blue wire will then just be spliced into the reverse circuit wire behind the tail lights. If your trailer doesn't already have a 5-Way, the above mentioned harness # 20017 will work perfectly.

Dennis

2/24/2026

I have a 4 pin plug on my trailer and a cargo rack which goes into the trailers rear receiver with a 4 pin plug. How can I convert this set up to a 5 pin so that I can put backup lights on my cargo rack to assist in backing up the trailer?