How to Wire 5-Pole Trailer Connector on Hitch Cargo Carrier to Match 5-Pole Vehicle Wiring

Question:

I have a 5 pole trailer plug on the back of my car. I just bought a “hitch hauler” that has some brake lights mounted on it with a 4 pole plug. Would the do they sell a “5 pole to 4 pole adaptor?” All I can find is the 4 to 5 adapter, which reads “convert your vehicle’s 4 pole into a 5 pole....” However, I need to do the opposite....?? What adapter should I buy? Thanks.

asked by: Jake

Expert Reply:

4-pole flat and 5-pole flat trailer wiring harnesses actually use the same function-to-pin configuration for the three basic lighting circuits they have in common. These three are left stop/turn, right stop/turn and running light circuits.

If a 4-pole and a 5-pole can be physically connected together, meaning if their plug shapes fit together without interference from the molded plastic housings, they'll work together just fine without need for an adapter. On some plugs it may be necessary to use a utility knife to trim some plastic to let them connect. This simply means one of the contacts on the 5-pole will be left exposed (not connected). The pins for the grounds (for the white wires) have to join together for any function to operate.

If you like you can install a new 5-pole # HM47910 on your carrier's wiring using crimp-on butt connectors # DW05744-5. You can refer to the linked article on wiring for a guide to making the connections. I recommend using dielectric grease # 11755 onside the butt connectors to block out moisture that can cause connection issues over the long term.

expert reply by: Adam R