How to Make an Adapter to Go from Semi Truck 7-Way Round to RV Style 7-Way Blade on Trailer
Updated 07/01/2024 | Published 04/07/2015
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Question:
In another thread on this site an expert said from semi to rv plug an adapter was needed, and a different expert said just the recepticles are needed.do i need an adapter, and which one to haul trailer with 7 way flat rv type plug with a semi tractor. Thanks.
asked by: Todd
Expert Reply:
Either way is correct. It depends on if you want to keep the semi-style 7-Way (if you need to tow that type of trailer) or if you will never be towing a semi-trailer.
If you need to keep the 7-Way semi active on the truck, then you would need to make an adapter to get it to work with an RV 7-Way. For that you would need a trailer side 7-Way round, # PK11702, a converter, # RM-732, and a vehicle side 7-Way RV style, # PK12-707E.
A semi-7-Way has separate circuits for the brake lights and each turn signal. And RV style 7-Way has the brake lights combined on the same circuit. So, what you would do is use a circuit tester such as # PTW2993 to determine the functions of the 7-Way on the tow vehicle. Then you would place the red wire from the converter to the appropriate spot on the back of the trailer side 7-Way round for brake lights. Do the same with the green wire for right turn signal and the yellow wire for left turn signal.
You will also need additional wire to attach to the back of the 7-Way round for the other functions needed. For ground and 12 volt power you can use # 10-2-1. For running lights you can use # 16-1-1, and for electric trailer brakes use # 10-1-1.
On the output side of the converter you will attach the wires to the back of the vehicle side RV 7-Way. The green wire will attach at the 9 o'clock position, yellow goes to the 3 o'clock position. Ground goes to the 5 o'clock position, 12-volt power goes to 11 o'clock position. Running lights goes to the 1 o'clock position. The center pin is for reverse lights which is uncommon on many trailers. But if needed you will attach some wire to the appropriate pin on the 7-Way round pin and attach it to the center pin on the back of the RV style 7-Way.
I would then wrap up the whole sha-bang in electrical tape and voila; you just made an adapter.
The alternative is to replace the 7-Way round pin on the vehicle with a 7-Way RV style connector. You could still use # PK12-707E and converter # RM-732. What you would do is remove the 7-Way round and then use the circuit tester to determine the functions of the wires. After that you would hook up the converter wires and other wires as explained above and mount the new 7-Way to complete the installation.
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Caleb
6/30/2024
running the additional wire for brake lights to green and yellow (signal wires) then causes a conflict between your signal wires because your essentially looping them...how can this be mitigated?