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Brake Controller Pin vs 12V Power Pin for 7-Way on 2016 Mercedes-Benz GLE 350

Question:

I have an MB GLE 350 2016 with factory hitch and plug. I want to tow a small 3000-4000lbs rv trailer with electric brakes. Im told that the seven prong plug does not have 12-volt power it behaves like a four-prong plug, however, the owners manual says permanent power is supplied to trailer socket pin #4. Your site says the following: If you have a factory 7-Way wiring connector on your GLE-Class 350 then you simply need the Plug-In Adapter # 3066-P for a Tekonsha controller like the Prodigy P3 # 90195 which installs on a connector that can be found under your drivers side dash behind that carpet that is behind your brake pedal. This suggests that I dont need to hardwire 12 volts to the factory plug. Please clarify.

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Expert Reply:

The 12V power that you are referring to is actually on a different circuit than what your Prodigy P3 # 90195 and the Adapter # 3066-P will be sending power on. The 12V power is constant and is the pin in the 2 o'clock position while the brake controller will only send power when the brake pedal is pressed (while you're traveling) or if you apply the brakes with the manual override. The pin for the brake controller is in the 5 o'clock position for the 7-Way connector on your 2016 Mercedes-Benz GLE 350.

I'm not sure how you would connect the 12V power unless there is already some wire running from the 7-Way connector to your battery and you just need to make a connection (some pickups are configured this way) so your best bet is to contact your local Mercedes-Benz dealer and see what they say.

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expert reply by:
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Jon G

Question:

Jon, Thanks for answering my question.MB does not provide power from the battery to pin 5, therefore, hardwiring from the battery to the socket is required. The MB dealer will not do this wiring so the car must be taken to a qualified RV dealer; I've been quoted a price of about $450 for the wiring. Thanks,

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Expert Reply:

Oh please tell me you haven't taken them up on that...hardwiring and routing some wiring can be a pain sometimes but it isn't THAT difficult. It's more time consuming than anything. They are likely charging you for multiple hours of labor at a high price.

All you need is the appropriate length of 10 Gauge Wire # 10-1-1 (sold by the foot), a 40A Circuit Breaker # 9510, and some wiring connector supplies like what you find in the Hopkins Deluxe Trailer Wiring Installation Kit # HM51020. If you use these supplies you can route the wiring yourself from the positive terminal of your battery to the 7-Way at the rear of your vehicle. I have attached a helpful article on this subject that you can check out as well.

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expert reply by:
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Jon G

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