super7pilot

I was shopping trailers while living in Germany. Some interesting units over there. Same with the UK units. Of course there was the opposite issue when cars started to commonly use separate amber turns & the US trailers had ( still have) the old one bulb twin filament setup. As I recall. All the German & UK trailers I saw had surge brakes as opposed to the in car brake controllers. Much simpler & solves any issue with electronics.

I called Curt this morning about a load distribution set up. They said while it would work. It really wouldn't solve the light MB tongue weight issue. The load distro setup would transfer weight back onto the trailer. But the setup weighs in at 80 Lbs. It's meant more for a very heavy tongue on a larger truck to level out the trailer for better tracking. But has the side benefit of also reducing tongue weight a bit.

While on the phone I also asked about the electrical issue & how they mitigated the lights out warning on the new computer controlled systems on new cars. Their setup operates very similar to the old ignition timing lights. They use a totally separate power supply from the battery to power the trailer lights. And uses a relay system that just uses the tail lights as a trigger signal & not the power source.

fabbrisd1

Yes - proper trailer light wiring runs up to the battery - the LED light deal can be thought of as a bit separate - for LED's/match - often the solution is a simple adapter plug avail from internet trailer houses that has built-in resistor which solves that LED issue..

super7pilot

Agreed, But as the trailer power is separate from the computer monitored OEM lights power circuit. As well as the Curt converter not providing a resistive load that the OEM computer will see. Which "in theory" should prevent any issues. It's akin to having a CB/Ham radio or subwoofer power amp that's powered from the battery on it's own fused circuit but has a on/off relay on the ignition/accessory power wire to prevent battery run down. The computer shouldn't even know it's there. But as in all things. One's mileage may vary and strange things can happen.

Forgot to mention, I hooked up a trailer to my new Curt hitch & wiring. It was a U-haul trailer so was probably the worst case scenario as far as abused and shoddily patched up trailer lighting. I'm happy to report that the sun didn't go supernova, The sky is still in the sky, And my GLK worked fine with no faults or lights out reports and did not spontaneously combust.

PPS, I also called MB about the tow kit. It consisted of the hitch, Wiring & an extra duty cooling fan. NO OTHER MODS. No additional capacity trans coolers or engine radiators.

super7pilot

Just got back from Canada (Vancouver Island) where I had my car trailer made. Happy to report that all went brilliantly. The Curt wiring converter worked as it should have. No faults or bulb out warnings. We were moving along I-90 over the Cascades (Snoqualmie pass) which has a rather long steady climb, I had the cruise set @ 70MPH. The GLK250 never down shifted from 7th gear & returned 34MPG, The temp gauge never varied from it's normal non-towing temp. Here is the trailer I bought to haul my Caterham. https://www.flickr.com/photos/130801...57657338250809

HONDO250

Great to hear when an after market install works out to the owners satisfaction.
Happy travels

MRGLK

Any chance you can post some picutres of your install and wiring? If your feeling real adverntourous perhaps a video all hooked up and working? Just to give the rest of us some hope?

super7pilot

I might try and take a pic of the hitch. But the wiring is hidden out of the way (as it should be)
There was nothing special about the install. The key ingredient in preventing a bulb out reading, Is to use a powered converter. It takes it's power from the battery and uses a trigger wire from the tail lights. It does not use the tail lights wires as the power source thus will not increase the load that the MB brain sees. Which is what triggers the fault reading.

The install was done by a local independent muffler/hitch shop. I did not lay a hand on the GLK. They ordered everything from a Curt supplier. The hitch is a Curt 13155 here is a link to the hitch. Just click on the install instructions and a PDF will down load for you to look at. LINK

CBR Dude

I wanted to ad lib here. Not that you want to hear any more input on this. I've had the GL450 and now the GL550. Never had an issue with the GL450 pulling the trailer or the lighting. The GL550 has been nothing but a PITA. Still unresolved. I've had the truck to Mercedes twice. With no results. I've had it to a trailer shop twice. Both are dumb founded as how to correct the problem. The trailer shop has bought two of the Tow Ready adapters specifically made for this application for German cars. The problem lies with the LED lights on the trailer do not pull enough juice and therefore trip the SAM into thinking the bulbs are out. The first one stopped the hyper flashing, the second one still produces the bulb out indicator on the dash. Mercedes has warned me that if I cut into the OEM harness they are out of the game on warranty issues. They had no solution what so ever other than telling me that. Useless is what I'd call it. The trailer shop wants to cut into the harness and install a resister. I'm not in favor of that until my warranty runs out. For now I have to live with the lights out indicator.

I just have to vent and say this is the only car manufacture I've had nothing but lazy service techs and unwillingness to get at the root of a real simple small issues like this that are driving me insane.

When I'm done with this mechanical monster, it's back to the rice burners.

super7pilot

Several trains of thought CBR. Are the tow ready adapters the ones that go from a seven pin to a four pin? As a last resort why not just have the tail light converter added to totally bypass the overly complex fatherland nanny state wiring & be done with it?

As an aside. I asked my dealer about installing the OEM MB hitch. They nearly choked on their coffee at the $3k + price tag of installing the factory hitch setup and were the ones to suggest an after market one with the converter.

To be honest with you & this has nothing to do with you personally CBR. Generally speaking, It's what we folks deserve for being so utterly lazy that we can't even be bothered to do a light check while sat in the garage where you can see if a light is out. No instead we want the car to check them for us, We also can't be bothered to look before backing up, Or doing a lane change. We have nannies do that for us.
Before long we will be complaining about having to wipe our own bums.

I'd also like to ask. Why go from a 450 to a 550? They can tow the same 7500Lbs but at a 10MPG penalty with the 550.