C36 AMG - Unknown part

[eddie]

While working on my car i found a part unpluged, it was in the boot under the carpet and plastic cover. When i pluged it in the indicator lights came on and stayed on, so i called Merc's and aksed what it was for. They said it was a control unit but did not know what for? I bought a new one and pluged it in the indicators do not come on now but there is no differance in the car the part is no:140 820 66 26 the car is a C36 AMG 1996 model. Can anybody tell me what it is for.