Warning buzzer switch - Central door locks??

[rgnprof]

I have tried to fix a central lock problem on my '91 300CE for a month now - 2 brand new Hella pumps, used ebay one, troubleshooting etc. I have a new pump installed, but I'm not getting it to run when I turn the key, even though I have 12v to the pump. I am assuming that when I turn the key - either to lock or unlock - current isn't flowing to ground and then to 12v. None of the doors or the trunk are activating the pump...so I'm assuming a bad electrical connection somewhere.

According to the FSM wiring diagrams, the warning buzzer switch on the steering column is a possibility. Does this sound possible - and how can I check the switch?

ryan