I've been going over wiring diagrams for my 97 SL320, same engine as your 96 but with ME 2.0 / ME 2.1 ECM so your colors may be different and possibly relay operation different.

K17 is the relay block

pin 8 red is a relay contact arm and is fed from circuit 30

pin 2 gray / brown is a relay contact and feeds the air pump

pin 6 brown / purple the relay coil and runs to the ECM

pin 4 red / green is the relay coil and leads to circuit Z7/36

I don't have good data as to if the ECM applies power to pin 6 or pulls it to ground.