Quote

8) The signal coming out of the ECU at C-40 on the BW wire is the coil trigger to close A/C Relay A. NOTE this is a 12v(-) trigger to complete the relay coil's ground path through the ECU.

Try it with above grounded.
I do not have the proper manual so I was looking at a 1990FSM and they do not go into the ECU that year.
I will try to find the proper diagram in the morning.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.