I thought it is some kind of gearbox controll thing.
I fined in a electric diagram for E34 m5 3.8, there is 2 version of cabeling. With EGS and whitout EGS.
With EGS wersion in the gearbox installed a 3 pole switch . 2 pole for the reverse light and one pole for the "EGS". Maybe on neutral gear position the dme use a diferend setting for timing and fuel?