Fish--

What year is your 124? It's not listed in your signature.

The pump should work at all times (key in or out, engine running or not). This suggests that someone may have boogered your wiring. The pump should have power at all times from Fuse C (pin 3 of the rectangular connector at the pump should have a red/white wire and it should measure +12 Volts at all times.

Pushing or pulling one of the buttons (or turning a key in that door) not only locks/unlocks that door but switches a switch in the door that tells the pump to run, creating vacuum to lock all doors or pressure to unlock all doors. A round plug at the pump has three wires (blue=driver, green=passenger, yellow=trunk/tailgate). One of these wires could have broken where they go through the rubber accordion sleeve between the front doors and the A-pillars.

If you are losing pressure/vacuum you may have a bad diaphragm in one of the actuators. The fuel flap lock is often mentioned as a culprit. You can disconnect its line and test the actuator with a Mityvac to see if it leaks. Another option is to blank off that line (flap will no longer lock) and see if the system now works.

Many other options but try those first and report.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970