2002 E430 (W210)

Experienced strange sequence of events leading to no start condition... initially lost Xenon headlight function.

Subsequently renewed starter battery (under rear seat), due to age, but lost all exterior lighting function at that point, as though light switch had failed.

Discovered plastic housing of headlight control unit (under rear seat) to be substantially heat deformed. Unable to determine its functionality.

Afterwards, unable to start the vehicle with either of two known good Smart keys... insertion of either key resulted in no appropriate click nor ability to rotate key within switch.

Exchanged existing headlight switch with functional unit but recovered no exterior lighting.

Central locking is inoperative, whether commanded manually or with Smart key.

Does the EIS have control over function of the vehicle's exterior lighting?

Is there a master fuse controlling the EIS?