M-Class (W166) 2012, Read about the upcoming M-Class

Towing issues (sorry, long)

Old 07-27-2012, 04:08 PM
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ML 350
Towing issues (sorry, long)

I am looking for advice and maybe I will shed some (hence the length, sorry). Have a 2012 ML 350 Bluetec and a Haulmark 18’ cargo trailer. At first, the 350 would not “see” the trailer or said there was a fault in its left turn signal. We had no brake lights, turn signals, or night lights on the trailer. Solved this problem, which I thought was due to not enough current being drawn by the trailer’s presumed LED lights, by installing a Valley 39010 wiring adapter.

I then tackled the trailer electric brake controller issue by installing a wireless Prodigy RF on the trailer. Found I did not need the Valley adapter too, as the Prodigy plugged into the 7 way outlet and effectively served the same purpose. Tested all lights (including trailer running) and was good to go. Did a 150 mile tow in daylight and the combination was awesome – averaged nearly 17 mgp and the 350 was a beast, accelerating up hills, etc. All good.

However, when I returned home a few days later, I lost all lights to the trailer (except right rear brake, I think - I was alone) at dusk when I first tapped the brakes with the trailer lights on. Fuse F130 had blown. Called roadside assistance to find there were no spare fuses of any type in the SUV. “Borrowed” one from the rear 12V outlet and started off. This one blew ten seconds later. Then another. Finally, I ended up leaving the trailer and spending the night at a local motel.

The next am I took the trailer in daylight to a MB dealer 35 miles away and we studied the factory wiring diagram. The wire for fuse F130 is only suitable for 20A so an upgrade in fuse to 30A was not feasible. The Prodigy says it wants 20A (not sure it uses all that) and the trailer electrics, between brakes and lights, an unknown additional amount -Haulmark hasn’t returned my calls! Why are technical manuals so hard to find or don’t include the data!!?? Maybe they aren’t LED like I first thought. Dealer says he thinks they are incandescent. Manual say I have DOT Ext. Lighting/Dbl. Bulb. (??) Thanks a lot. That would explain the fuse blowing, but not the inability I had at first “seeing” the trailer without the Valley adapter…

However, now despite the fine efforts of a great MB dealer in New London, CT, I couldn’t use both the electric brakes and the trailer brake lights at the same time (fuse F130 blew in daylight) for some reason, so I had to choose between one and the other. Chose having the trailer brake lights (with my original Valley adapter) and trusted the 350’s solid brakes to do the work, driving slowly and leaving lots of room ahead on the highway. No problem.

The factory wiring for a fixed brake controller (not RF) is apparently 30A capable. So, it appears I am forced to have dealer install a trailer brake controller by the dash, rendering my RF useless. I don’t know if this 30A wire will run the trailer lights too or if they are still going through F130. Not sure it matters much. Made sure to buy spare fuses the next day…

Anybody have this experience and have any advice on how to proceed? Any work-arounds? Hope this is of help to some, and don’t forget to carry spare fuses…
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Old 07-28-2012, 09:16 AM
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2018 GLE 43 SUV
This thread covers the DIY installation of a trailer brake controller utilizing the existing towing-package connector.
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Old 07-29-2012, 09:04 AM
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Originally Posted by Shrdlu View Post
This thread covers the DIY installation of a trailer brake controller utilizing the existing towing-package connector.
Thanks for the reply. I am the person who contributed the four pictures where to find the controller harness wires, so I am aware of the thread.

Guess I am wondering if anyone else has had a problem with the combination of a large trailer (maybe a dozen small night driving lights around it, four tail lights, and electric brakes) and a wireless Prodigy RF controller. The 20A power to the trailer (without setting up a wired brake controller) evidently doesn't cut it on its own when all are in use at the same time.

Am trying to avoid going the wired brake controller route with a MB dealer if a solution is offered here...
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Old 07-29-2012, 04:28 PM
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'13 ML350 Bluetec for work, E550 for pleasure, & ML350 for my wife
I have a 10K rated dump trailer with LED lights.
I tow with a 2010 GL450 using the Prodigy wireless controller.
When my GL's lights are on, the LED's on the trailer all flash until I apply the brakes. When GL lights are off all lights work normal.
The "Deep Cycle" (?) battery on the trailer appears to be charging properly while the vehicles are connected through the 7-way.

I will say I really don't like this RF controller's drive feel as well as more conventional controllers I've used in pickup's in the past. Next SUV I buy I plan to go back to a conventional unit, like the Tekonsha Primus IQ
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