Mercedes sure does not make it easy to tow with their premium priced large SUV

I bought a Bri-Mar trailer last week, equipped with electric brakes & LED lighting. In preparation, I had ordered a Tekonsha Prodigy RF Trailer Brake Controller # 90250, a unit that received good reviews from other GL owners.

The advantage of this unit is a wireless radio control, which supposedly does not require any drilling, splicing, or modification of any type. This sounded great, as the vehicle is leased.

So on Sat, I drove to pick up the trailer, with all the componants & a few tools which with to mount the unit onto the trailer.

First failure was the inability to pair the trailer mounted power box to the vehicle remote, which plugs into any 12 v lighter outlet. Hence, no powered brakes.

The second failure was the trailer lights. They came on, but only in a constantly flashing mode. I did get brake & turn lamps, but with the other flashing lamps all over the place, I decided driving the thing 50 miles home would be pretty stupid.

Research has educated me that MB, as well as Volvo, Audi, Porsche, & VW all have problems properly working with trailers equipped with LED lighting.
One maunfacturer, Valley, offers an adapter that has some resisters that trick these "oh so smart" german cars into believing that normal incandescent lamps are on the tow vehicle. Guess what. No one has the unit in stock, and the manufacturer will not have more until mid June.
Meanwhile, here I am stuck with a trailer I can't use because my $60K POS German engineered "tow vehicle" is too fricking smart.

Do I sound pissed? That's because I am.

I've yet to call the MB stealership to see if they can offer a solution.

I've tested the leads on the factory 7 prong trailer wire receptacle.
Lead #4 (12v battery power) is indeed live when the engine is started.
Leads 5 & 6 are energized when the brakes are applied, and flash when the corresponding turn signal is switched on.
Lead 1 is a good ground.
Lead #2 is NOT energized. Please correct me if I'm wrong, but I understand lead 2 to be the varying output brake lead used on a conventional harness mounted brake controller, and as such it is acting normally, as no controller is installed. (?)

Any light anyone can shed on this situation would be greatly appreciated.

David in MD

No problems here towing an LED light equipped trailer on a G500. Towed it on several occasions, and works without a hitch.



IIRC, the 7 pin plug is supposed to carry trailer brake signals.

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-Justin

91 560 SEC AMG - other dogs dd
01 Honda S2000 - dogs dd
07 MB ML320 CDI - dd
16 Lexus IS250 - wifes dd

it's automatic.

Play the numbers: the VAST majority of trailers do NOT have LED lighting.

In addition the VAST number of cars/trucks do not have bulb-out indication for trailer lights as does your Mercedes.

My trailer with conventinal lighting worked fine first time ... which was great because I purchased it about 2K miles from home.

If all your trailer brake system requires from the vehicle is 12V power, any problems are obviously not created by the vehicle. Surely you need signal from brake light circuit ... which is altogether another thing.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles