How To Install a Trailer Hitch on a W211 Wagon
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From: Nova Scotia, Canada
2003 CLK430 Cabrio, 2009 BMW 535 iX Wagon
How To Install a Trailer Hitch on a W211 Wagon
This is my experience installing a Curt 11820 hitch and a TowReady 119176 harness in my 04 E500 Wagon with Sport Package (i.e., with LED tail lights) and without Keyless Go. Much of it may apply to the sedan and post-facelift cars. There are forum posts across the internet suggesting that Keyless Go may require you to remove the bumper cover. I did not have to, but it might have been easier...
I backed the car onto ramps, which gave me easily enough clearance for the job. Obviously, a lift would make a few things less tedious. The installation of the trailer hitch was almost as smooth as the instructions suggest: http://www.etrailer.com/instructions.aspx?pn=11820. The one thing that caught me off-guard was that, while wiggling the hitch in place, I pushed one of the vertical screws all the way into the bumper beam. The screw head is very hard to reach to push the screw back down, and the slot in the hitch was off by a fraction. After a lot of blood, sweat and tears, I ended up using a crowbar to bend the bumper support over a bit, and that did the trick. So if you do this, pay special attention not to push the vertical screws up too far. I do not think duct-taping them down or something would work reliably, but it may be worth a try. Without this issue, the mechanical installation would have taken less than an hour, with ample time to tidy up and having the obligatory beer.
Same for the electrical installation: Knowing what I know now, I could do it in maybe 45 minutes. But, of course, it took me a lot longer. During my pre-purchase research, I had read somewhere that the Curt 56146KIT does not work with LED lights on the trailer. And I head read somewhere else that the TowReady 119176 works with LEDs on both the car and the trailer. And it was my own fault that the latter does not seem to be the case, and I ordered the harness with the cheapest supplier rather than the one that claimed it does work.
To cut a long story short, the 119176, which contains the supposedly upgraded controller labeled 17499-204, does work with PWM-controlled LED tail lights in the Sport Package Wagon. But the instructions do not tell you how. The left tail light has two relevant wires: The one in the bottom of the connector controls both tail and stop lights. I seem to recall it is black with a red stripe. Connect this to the tail light wire of the control module. The one on top controls the left turn signal. Connect it to the respective wire on the control module. I believe this one is yellow with red. The one in the middle is ground (brown with white, for sure).
Now comes the tricky part: The stop light is also controlled by the bottom wire, and the 17499-204 control module does not distinguish between the shorter pulses that make for tail light mode and the longer pulses that make it the stop light. So connecting the stop light wire there does not get you anywhere. The stop lights on the trailer will blind traffic behind you whenever the tail lights are on. To cope with this, I used a trial and error approach to find the wire that controls the stop light in the Mercedes OEM trailer wiring.
There is a Y in the the wire harness inside the left cargo area compartment, just underneath the tail light. Since you probably removed the tail light, you would have this area accessible anyway. One branch of the harness goes forward, one aims toward the threshold of the cargo area and over to the right tail light, and the third one heads up, also supplying the left tail light itself. Open the branch that goes over to the right. The green wire with the yellow stripe is the stop light signal. Conveniently, you can tap the right turn signal (black with green) and the power supply (large-gauge red) in the same location. No need to run a wire across for the right turn signal. Side note: These colors are for sure, I only neglected to take note of the two by the tail light. You may even be able to tap all signals right by this Y rather than by the tail light connector.
The rest is very straightforward: There are at least two solid ground points underneath the Nav DVD drive. After cutting the trailer harness and inserting a four-pole connector, I used the smaller one of the two feed-throughs underneath the tail light to route those wires out. And the rest goes per the instructions (http://www.etrailer.com/instructions.aspx?pn=119176).
As I said, knowing what I know now, the whole job would be done in far less than two hours. I hope this write-up will save one of you forum members a little time or a few gray hairs...
I backed the car onto ramps, which gave me easily enough clearance for the job. Obviously, a lift would make a few things less tedious. The installation of the trailer hitch was almost as smooth as the instructions suggest: http://www.etrailer.com/instructions.aspx?pn=11820. The one thing that caught me off-guard was that, while wiggling the hitch in place, I pushed one of the vertical screws all the way into the bumper beam. The screw head is very hard to reach to push the screw back down, and the slot in the hitch was off by a fraction. After a lot of blood, sweat and tears, I ended up using a crowbar to bend the bumper support over a bit, and that did the trick. So if you do this, pay special attention not to push the vertical screws up too far. I do not think duct-taping them down or something would work reliably, but it may be worth a try. Without this issue, the mechanical installation would have taken less than an hour, with ample time to tidy up and having the obligatory beer.
Same for the electrical installation: Knowing what I know now, I could do it in maybe 45 minutes. But, of course, it took me a lot longer. During my pre-purchase research, I had read somewhere that the Curt 56146KIT does not work with LED lights on the trailer. And I head read somewhere else that the TowReady 119176 works with LEDs on both the car and the trailer. And it was my own fault that the latter does not seem to be the case, and I ordered the harness with the cheapest supplier rather than the one that claimed it does work.
To cut a long story short, the 119176, which contains the supposedly upgraded controller labeled 17499-204, does work with PWM-controlled LED tail lights in the Sport Package Wagon. But the instructions do not tell you how. The left tail light has two relevant wires: The one in the bottom of the connector controls both tail and stop lights. I seem to recall it is black with a red stripe. Connect this to the tail light wire of the control module. The one on top controls the left turn signal. Connect it to the respective wire on the control module. I believe this one is yellow with red. The one in the middle is ground (brown with white, for sure).
Now comes the tricky part: The stop light is also controlled by the bottom wire, and the 17499-204 control module does not distinguish between the shorter pulses that make for tail light mode and the longer pulses that make it the stop light. So connecting the stop light wire there does not get you anywhere. The stop lights on the trailer will blind traffic behind you whenever the tail lights are on. To cope with this, I used a trial and error approach to find the wire that controls the stop light in the Mercedes OEM trailer wiring.
There is a Y in the the wire harness inside the left cargo area compartment, just underneath the tail light. Since you probably removed the tail light, you would have this area accessible anyway. One branch of the harness goes forward, one aims toward the threshold of the cargo area and over to the right tail light, and the third one heads up, also supplying the left tail light itself. Open the branch that goes over to the right. The green wire with the yellow stripe is the stop light signal. Conveniently, you can tap the right turn signal (black with green) and the power supply (large-gauge red) in the same location. No need to run a wire across for the right turn signal. Side note: These colors are for sure, I only neglected to take note of the two by the tail light. You may even be able to tap all signals right by this Y rather than by the tail light connector.
The rest is very straightforward: There are at least two solid ground points underneath the Nav DVD drive. After cutting the trailer harness and inserting a four-pole connector, I used the smaller one of the two feed-throughs underneath the tail light to route those wires out. And the rest goes per the instructions (http://www.etrailer.com/instructions.aspx?pn=119176).
As I said, knowing what I know now, the whole job would be done in far less than two hours. I hope this write-up will save one of you forum members a little time or a few gray hairs...
