I don't know what year your working on but on the 2000, there is a fuse that needs to be installed in position #18. It is 25 amps. This furnishes the power to the brake light, turn signal module.

After reading all this, and seeing what the wire harness cost, I decided to get a factory unit. Took less than an hour to take the bumper cover off, bolt everything up, connect the wiring harness, put the cover back on, and put the fuse in.

And already towed a trailer over 400 miles. Sweet.

__________________
Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport

I just got back from a boat rally 1000,00 round trip did not do good on gas going up hills in 4th, on the way back left it in drive and got way better gas milage. Ran much better did not have to add oil.

Make sure that you do the smart thing...Take off the back cover on the driver's side and plug in the harness to the pre-installed connector. I have an ML320 that I purchased from my father-in-law that already had the towing package installed. I couldn't for the life of me figure out why the trailer lights wouldn't work (had the fuse and relays and everything checked). Finally one of my buddies pointed out to me that I didn't have the damn things plugged in.

Keeping the world smarter than me-

Chris Warner, Lt, USAF
AC-130 Pilot

Wow, it took me more than a few days but I got around to doing this install last week, it did not go smoothly but thanks to MLCharlies help I was able to finish it. I'll post his very helpful instructions below.

One comment though about the parts prices listed by Jordy, they are *not* California prices...must be related to the real estate market somehow

The dealer harness and connector adaptors and mounting bracket all totaled about $150-$160 and added parts not needed for most applications. I used the $29 Modulite 18187 and I have a simple and cheap way to haul any trailers with flat 4way plug.

One modification to MLC's instructions is that the factory plug may not be behind the rear panel opening. Mine was behind the side panel almost at the hatch, I ended up removing the driver side rear panel to expose the wiring. Another would be to not try to fashion a connector to the factory plug or solder anything but instead simply use wire snap connectors. These are less intrusive to the factory wiring and will work well.

Here are the instructions...


You have to look real close on the connector to see the small numbers imprinted on it. Below are the wiring colors. You can always use a 12v test light to determine the wiring layout.

The connector you a looking for is in the first aid kit compartment, down at the bottom and benind the fuel filler piping. It can be hard to find, there is nothing else plugged into it.

When you find it and facing the connector you will see it has a top set of numbered female terminals and a bottom set of numbered female terminals.

The posted info will make more sense once you find the connector :

You can use a Draw-Tite ModuLite # 18187, and interface between the ML electrical system and your trailer lights.

Inside the LH cargo area access panel is a spare female wiring connector that will have the wiring you need to access.

Facing the connector, top terminal # 1 is +12VDC and #2 is -12VDC.

Install a 25a fuse in the underhood fuse box position # 18, verify, to provide battery power to the connector.

Facing the connector, bottom terminal #1 is -12VDC, terminal # 2 is tail light, terminal #4 is LH turn, terminal # 5 is RH turn and terminal # 6 is stop.

The ModuLite input wiring ends can be soldered and inserted into the ML connector terminals, tape and nylon wire tie securely in place.

Connector # Wire Color Function Modulite Wire Color
---------- ---------- -------- ------------------
T1 Brown - 12VDC White
T2 Red + 12VDC Black

B1 Brown - 12VDC
B2 Blue Tail Light Brown
B4 Green LH Turn Yellow
B5 Red RH Turn Green
B6 Stop Red

T=TOP
B=BOTTOM


The ModuLite output wiring is extended through a rubber grommet to below the vehicle.

You will need to cut the grommet to install the trailer wiring/plug and use a silicone sealant to glue/seal the cut grommet back together in place.

Use a test light to verify all of the above wiring connections.

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

I skipped the factory wiring harness, plug, and receiver and bypassed the relay in the fuse box. Had installed a DrawTite receiver, 2” drop draw bar, break controller and both a Bargman 7-way plug and flat 4-way plug as well. Total parts and labor came to around $450. Going through the factory relay with non-OEM parts was a pain; so direct connect to the battery solved that problem. Mercedes wanted $1200 for the parts and labor and that certainly was not going to happen.

-Kevin