Converting 7-Way On Semi To Work With 7-Blade And Operate Electric Brakes
Updated 10/22/2025 | Published 04/01/2025
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Question:
Good morning, I have a 1997 Freightliner Fld120 Daycab semi truck that Ill be using for a mobile truck washing business. Ill be pulling an enclosed trailer with your standard blade connector. Truck has a 7 way pin. What do I need to purchase to convert the 7 way pin to blade so everything works properly? Also, enclosed trailer is equipped with brakes so Id also like to wire up brakes. Its a bit overwhelming to see all the products related to this, I just dont know what to get. Thanks in advance.
asked by: Juan
Expert Reply:
Hello Juan, thanks for reaching out. There are a number of factors involved when converting a semi 7-way to an RV 7-way. Semis generally use a 7-pin round pin socket, similar to # PK11720. And RV style 7-way uses blades, like # PK12706. We do not offer any pre-made adapters to make this conversion that will carry all of the electrical functions required by the RV.
Another thing to be aware of is fifth wheel trailers use a combined wiring system where the brake lights and turn signals are on circuit. Your semi connector uses a separate wiring system where the brake and turns are on different circuits.
Also the brakes on your trailer are likely electric brakes and your semi 7-way is not wired to power them. The brakes on a semi are typically air brakes, and are controlled through a different connector than the 7-way. You will need to install an electric brake controller in the cab of your truck wired to the RV style 7-way to power your brakes.
If you want to keep your existing connector on your truck you can splice into the wiring. Or if you have no use for it you can cut it off completely.
To combine the tail light circuits of the semi you'll need a converter # 119250KIT. To install the actual RV 7-way use install kit # ETBC7 which will also include everything to install the brake controller. For a brake controller you can use the Tekonsha Prodigy P2 # 90885. You'll likely need additional wire # 16-4B-1 for 16 gauge which can be used on all tail light wires.
Attached you'll find a help article on trailer wiring as well as a diagram showing how an RV 7-way connector is wired.
(click to enlarge)
Product Page this Question was Asked From
Pollak Heavy-Duty, 7-Pole, Round Pin Trailer Wiring Socket - Vehicle End
- Custom Fit Vehicle Wiring
- Trailer Hitch Wiring
- Vehicle End Connector
- 7 Round
- Plug Only
- Pollak
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Jesse M.
10/22/2025
Hey Juan, how did things go getting your Freightliner wired with the RV-style 7-way and brake controller setup? Your update could make it easier for the next person trying to tow an enclosed trailer behind a semi.