left side footwell is the lock sensor. In case the compressor freezes/blocks, the water pump pulley would also fail, in case of such a failure the lock sensor will release the clutch from the compressor. That lock sensor is a bit high inside the footweel space behind the speaker. And next to it is the relais you are looking for, attached to the lock sensor
http://bmwe32.masscom.net/johan/ihka...sor_relais.jpg
You can find the relais and fuses in the ETM, usually around page 20 it starts where they show it, on the last pages there is even a component location chart/view
See here
E32 (1987 to 1993 7 Series) Wiring Diagrams
or here all on one page by built month/year:
Elektrik Relaisbelegung
all components
BMW E32/E34 IHKA System
Here another link which might be of help to you
BMWTIS -- Repair Information
check also my website below, many DIY write ups for the E32, especially the 750