The 12 V supply for the switches comes from the same place as the constant 12 V for the flat connector. So if you are having issues with the power feed then chances are the lock switches aren't getting their 12 V either.

Do you have a wiring diagram for the car? Go to Model 124 Maintenance Manual Index

There are inline splices in the wiring harness between the X30 distribution block (under the driver's side footwell kick panel) and the pump. Pwogaman had this problem:
http://www.peachparts.com/shopforum/3012362-post58.html

Or your wiring across the door hinge at one or more of the doors has flexed to the point of failure and shorted. Very common problem.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech