Adapting 7-Way Round Pin on Mack Semi-Tractor to 7-Way Blade Style RV Connector

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Question:

I have a 1997 Mack truck with 7 pin plug , I tow a sure trac trailer With a 6 slotted plug . How do I find a adapter or long cable with magnetic lights ?

asked by: John

Helpful Expert Reply:

A 7-pin connector on a Mack Tractor like you described would function a bit differently than a 7-way blade-style RV connector. The difference is the right and left turn pins on the 7-way blade also carry the signal for the brake lamps while on the 7-pin, one pin carries the right turn lamp, one the left and another carries the brake lamp signal. In order to combine those three signals onto two circuits, you'll need a taillight converter.

There isn't an off-the-shelf adapter that'll do what you're wanting to do, but you can assemble one. I'd recommend installing a taillight converter and a 7-way RV blade-style trailer connector on the Kenworth tractor. This way, you'd have 2 functioning trailer connectors.

I'd recommend using the # C59496 taillight converter which would tap into the circuits feeding your tractor trailer 7-pin round plug. The yellow wire taps into the feed for the left turn signal, the green into the right turn, the red into the brake the brown into the running light circuit and the white wire would ground to the truck's frame. The black wire connects to the positive battery terminal.

Once the # C59496 is installed, you'd then use an adapter like # 37185. The 4 pole from the converter would plug into the 4 pole on the adapter, then there'd be 4 loose wires to connect. Ground the white wire, the black wire connects to a 12-volt power source, the blue wire is used to carry the output voltage from a brake controller if the trailer has brakes and the purple wire is usually used for reverse lights. Other than the ground, if the other three wires aren't needed, you can bundle them up out of the way.

You could also use an adapter the # HM47425, and tap the # C59496 converter's inputs and outputs inline between the 7-way round pin and 7-way blade, but I believe the method outlined above would make for a simpler and cleaner install.

expert reply by: Mike L

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Willyd

1/19/2025

I have an 08 Ford F-350 super duty XL with a 7-way round pin receptacle. I need a 4 pin 5 pin flat adapter plug to connect to this to facilitate two smaller trailers that I have . The 4/5 pin flat adapter can accompany other modern adapters as long as it has the 7-pole round female at one end to plug into myy truck's receptacle. Thanks!