I have seen this done with a 30 and 40A relay. On the lower portion of the right fender you will find a block that has 3 or 4 wires inside. One of them is the start wire. I think most of them should be purple, but I am not for sure because I don't have the ETM in front of me.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS