How to Make a 7-Way Round Separate to 4-Way Flat Combined Adapter for Trailer Wiring

Published 04/14/2016

Products Featured in This Question

Roadmaster Brite-Lite 3-to-2 Tail Light Converter for Towed Vehicles

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$57.48

Pollak HD, 7-Pole Round Pin Connector w/Cable Guard

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$19.67

Wesbar 4-Pole Flat Connector w/ Jacketed Cable - Trailer End - 4' Long

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$15.72

Question:

I recently purchased a few four flat to seven pin round adapters , I have recently found that they will not not work properly with Volvo tractors, I have checked them on Kenworth and International trucks and they work .. is there a different wiring set up for these trucks? any help would be appreciated thank you

asked by: Randy S

Expert Reply:

Semi trucks can sometimes have different trailer wiring setups. I would be willing to bet that your Volvo has separate turn signals from stop lights and the problem is that the 4-way is designed for combined circuits where these signals are both on the same wire.

If this is the case you can build an adapter using the part # RM-732 as a signal converter.

You will need a round pin male connector, # PK11702 and then the part # W787264 for a 4-way. Basically you will be splicing the converter between these two to create the adapter.

The 4-way comes with 4 feet of wiring that would not need all of so you could cut half of the wiring off it to use to wire up the 7-way to the converter.

I attached a picture of a diagram that has how a 7-way is typically wired.