A/C condenser cooling fan problem.

Previously had my a/c condenser cooling fan hard wired to a switch and relay for manual aditional cooling (before my closed to open cooling system mod). Today wired it back to stock, but it wouldn't come on when the a/c was turned on. First jumped the fan to the battery, fan works. Then checked to voltage at the plug going to the fan with the motor running + a/c on, 0 volts. Anyone know where i should check next? Thanks in advance
blaise

'90 model 4.0/automatic DD