BlueRoy

2010 GL 350 Bluetec. Just bought new boat with heritage trailer. Trailer has electric brakes and 5pin plug. I bought the 7 to 5 pin adapter...it fits..but doesnt help the wiring...lights on trailer do not work. Anybody else have this problem and a fix?
Thanks,
Roy

dbtk

I ordered a 7 to 4 pin adaptor from Uhaul.com.

BlueRoy

Thanks, but its a five pin hookup for a boat trailer...didnt see it on Uhaul

StevethePilot

I assume you've checked with the local auto-part big-boys? (They have different names in different places, like Checker here now being called O'Reiley or some such, and AutoZone being something else in some other states, that kind of thing.) One of them ought to know what the wiring should be or if the problem's in the converter or the trailer, yeah?

When I got my trailer hitch (MB hitch attached afterwards, way too expensive to do it that way compared to ordering it for those curious), they included the 7-4 conversion only, so I don't know if MB even makes one that's guaranteed "right." Of course, it's worth it to know if the plug is correctly wired to begin with. Having either a trailer with a 7 plug or a volt meter, a friend and some patience can help in that area!

BlueRoy

Thanks again..just reached somebody at the merc dealership that is looking into it for me...will post his answer

Madcmm

Hey Blue does the trailer have LED lights if so buy a connecter like this http://www.etrailer.com/p-V39008.html. This has a resistor built into the plug that is needed to "trick" the MB sensitive electronics. I have this plug and use to pull my boat trailer equipped with LED lights and have no problems. The plug can also be used for non LED trailers and it converts 7way to 5 or 4 pin.

BlueRoy

Thanks, it took a little effort, but I found somebody at Mercedes that suggested the same solution. Just waiting for the plug now to see if it works.

///MONIQUE

Great info! I had the same issue with my 2010 GL550... my GL operated the lights on my 2009 boat trailer, which has incandescent lights and 5 pins (one for brakes), with a standard $5 adapter. However, the LED lights on my 2010 double waverunner trailer with 4 pins would not work. This adapter from etrailer.com ( part # V39008 $15 USD) solved the issue and works with both of my trailers! Please be aware that leaving the adapter connected to my GL without also being connected to a trailer- caused a "brake light" warning in the dash.

BlueRoy

Had Mercedes order in a 7 to 5 pin adapter with the resistance built in...works like a charm...bought 2 to keep a spare in the truck. Thanks again for the advice.

icerabbit

Looking at getting the Valley V39008 adapter (need to tow an LED trailer this weekend).

The product images online only show it being 5pin, which doesn't allow plugging in a 4pin cable connector.

How does it convert from 5pin to 4pin?

Does it come with two little rectangular insertable modules so you can pick either?

Thanks.

gbigpapa

BlueRoy, do you have a brake controller wired into to your truck? If not, all you have is running lights, turn signal lights, and brake lights but not actual brakes on your trailer.

Brocktoon

As a boat trailer, it likely has surge brakes. That is also why 4-5 pin, not 7.

gbigpapa

BlueRoy initally indicated the boat trailer has electric brakes and a 5-pin plug. 4-pin plugs are the minimum required for tail, stop, and turn lights. 5-pin plugs allow for another circuit typically for elctric brakes. 6-pin allows for an auxilary battery circuit (often to charge a break away switch battery or hydraulic pump battery for a dump trailer). 7-pin adds reverse lights or reverse lock-out for surge brakes. See link: http://www.etrailer.com/faq-wiring.aspx

Surge brakes are used on smaller boat trailers but you will often find electric systems on larger boat trailers. These systems are actually electric over hydraulic which use an actuator motor mounted up high which generates hydraulic pressure to the brake pistons. That way no electronic components get wet when launching the boat.

Therefore BlueRoy, if you have an electric brakers on your boat trailer you need to have a trailer brake controller installed to actuate them.

Brocktoon

If that's the case, it's a dangerous (perhaps illegal) trailer. I would not pull anything with electric brakes without a battery, and by extension a charging circuit. If you lose that trailer, it's a runaway. EVERY five pin trailer I have ever seen has been hydraulic or surge, never electric.

gbigpapa

In all likelihood his trailer has hydraulic surge brakes with the 5th wire as the reverse coupler lockout. In any case one should know exatly what type of equipment they are using on the road.

AMG3.2

delete

lkchris

DennisG01

I think the one you are referring to is actually a 6-pin? The 6-pin is 5 around the circle with a center, 6th pin. A 5-way is "flat"... all in a line.

lkchris

DennisG01

And...probably most importantly... this is a 7 to 8 year old thread