"A Possibility"
'could also be a broken wire in the conduit from the "A" pillar to the Door.
Welcome to the Wonderful World of ETM (Electrical Troubleshooting Manual)
Start Here:
http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/ETM/ETM.pdf
You want page 146.
[The Micro-Switch in the Trunk lock is successfully sending it's signal to the
Pump."ZomeZing" is interfering with the signal from the L / R door (s) M-S (s) .]