Troubleshooting Round 7 Pin Trailer Connection to 4-Way Flat Wiring

Question:

Round 7 pin to flat 4 adaptor Why do these made the way they are? None, no matter the manufacture, NONE, work for the brake lights. When I used then to connect to my car, which is wired with a flat 4 and used the adapter while towing my car behind a semi truck. Everything works but the brake lights

asked by: Keith

Expert Reply:

The 7 Pin functions are different on a semi than on a motorhome or truck. The 7-pin on your semi will have separate stop lamps from your turn signals, so you will need to combine them to have your trailer light function correctly. There is not an adapter for this as a wiring conversion is necessary.

You can absolutely use the Pollak Heavy-Duty Trailer Wiring Connector # PK11700 to connect to your semi, but you will then need the Roadmaster Brite-Lite Wiring Converter # RM-732 to take the separate signals and combine them for your vehicle connection with 4-way flat connector.

expert reply by: Jason S