525i Central Locking issue

Hi again
My '92 525i (RHD) manual's central locking is not functioning at all. I believe there are ways to check what the problem is by shorting various terminals on the central locking control unit. Does anyone out there know how? I don't even know where it is located! Please help. Thanks in anticipation...

I think its behind the floor speaker on the passengers side...thats where it is on the '88 535is...and the problem may have been caused by a short due to water due to a hole in the wheel well, thats what happened to mine