I bought an OEM one from the dealer. It came with everything, icluding a correct wiring harness. It was EASY to install - it came with very clear instructions. The only difficult part was cutting out the cover to fit tightly around the hitch. I used a dremmel and took my sweet time. Came out great.

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