Worth revisiting this post for those with a w124. After chasing intermittent operation of the central locking system from the trunk station, and (finally it failed completely) but not before replacing:

1. The trunk lock vacuum actuator and,

2. A known working convenience comfort control module.

The problem was the X48/F connectors in the right passenger footwell, particularly the red/red yellow positive power supply wires. Although the connector initially appears fine, once all the old hot glue shielding is removed, reveals totally corroded through, green separated wires!

I did not remove the front passenger seat, just removed the 4 seat bolts and tilted the seat forward to access the wire harness underneath the carpet.

This is also the power supply point for the passenger seat belt extender that stopped working. (see post: Seat belt extender 300ce)

I have some great pictures but they will not upload.