'99 Gaylander - Central Locking

Greets.
Hope I got the model right this time.

Was hoping to get some insight before digging into the dash --
central locking button does nothing. Remote works fine, opens
(and closes!) all doors. central locking button on the dash
does absolutely nothing. kaput.

the physical switch seems ok and the fuse is ok. Somewhere
in between something's gone terribly wrong.

any thoughts on possible culprit before i start sniffing around
all the wires?

'hanks.

3 connections to the switch on the circuit diagram. Center is earthed, and the other 2 go to the central computer. First thing I would do is check the earth connection is good, to E3 - connection said to be behind right hand rim panel. Measure resistance to bodywork to check.