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Just installed a factory trailer hitch on our 2010 ML550. Hitch was from a salvage yard. Time consuming, but straightforward.
I have the factory harness, but can’t quickly install it for a few reasons:
1) Rear SAM on the donor vehicle was in the right rear wheel well, my rear SAM is under the rear seat - need to extend the wires.
2) my rear SAM does not have the required socket - so I will have to change it out
3) there is a green plug that I believe controls the trailer electric brakes (if so equipped) - no corresponding plug on my ML550 - I believe I would have to run a new harness for this connection forward to somewhere in the driver footwell area
4) once installed, dealer programming would be required.
I don’t need electric trailer brake controls for the boat that I am buying. So I’m wondering why not just tap the taillight wires in the wheel wells for the three wires that connect to a std flat four plug connection. I’ve seen several kits that would allow me to make this connection fairly quickly and inexpensively.
checking with this group on a few things before diving in:
1) Will I be losing any important functionality by going this route vs. the new SAM/programming route? (other than the electric trailer brake controls which I do not need.)
2) Is there a preferred way to pursue tapping into the taillight wiring? I have seen lots of options spanning from a direct connection to a powered controller which takes signals from the taillight wires, but powers the trailers lights separately.
Thanks for sending all the process docs - nice to have them all consolidated in one place. I did already complete the mounting steps (see pic.).
Now I’m trying to figure out what functionality might be lost if I just tap rear light wiring for turn, running and brake lighting to the trailer (since I won’t need the electric brake controls for my trailer.).
Also wondering why I need to replace the fan - it’s already thermostatically controlled, so what functionality is added with the changeout.
Trailer bulb out detection.
Change in engine and transmission calibration (will hold lower gears to a higher RPM before shifting).
If you have ADS (adaptive suspension)- change in calibration settings, specifically stiffening up the rear.
Change in ESP calibrations and trailer sway control- if trailer sway is detected, the car will alternately brake the front tires to bring sway under control. <--- IMO the most important thing you lose
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