Unfortunately I don't have a schematic. From what you are saying, when I jump the a/c switch AND bypass the resistor, what I have is both fans running at high speed. The coolant temp switch should work when I disconnect the switch on top of the thermostat housing (remember, I have CIS-E injection). Therefore, it seems like the a/c circuit is working, but the high speed cooling circuit is not. Perhaps the coolant relay is broken. On my car the relays for the a/c circuit and the coolant circuit are different (you can't switch them to see if one works in the other socket), so even though I can hear the relays clicking, maybe the coolant circuit is bad.
So how about this: I just bypass the the drop resistor completely. This way, I know that when the a/c switch trips, both fans will engage and they will be running at high speed, and I don't have to worry about when or if my coolant circuit will kick in.
It was only 80 degrees today, and with the a/c on, sitting in traffic, my temperature was half way between 100 and 120 degrees. I know some say this normal, but my diesel never, ever goes above 95 degrees, so these temperatures make me very nervous.
This little modification seems like a decent solution to the high engine temperature issue on this car, especially since I can't do the mod possible on cars with latter fuel injection.