I need your Help (electrical problem)

[Oldschoolpony]

Ok, I have a 94,95,and 96 E350's. 2 of them are box trucks. The 94 has an odd electrical problem. The AC fan. The clutch and compressor works too. Problem is the Fan does not engage. I have checked the fan blower switch the resistor and the motor. Also the switch on the slider in the dash. I have no power at the fan. If i jump 12 volts to thr Red/yellow wire, the fan works. So somewhere somethings gone wrong. All the fuses in the 2 pannels are good. I cant seem to locate the fan.blower relay. Id like to test if a the relay is bad (which i doubt, I unplugged the compressor and you can hear the relay engage for the fan blower) I m trying to find out if the relay is getting power, or possibly the ignition switch is at fault. im trying to avoid going into the wiring harness and tracing back the hot wire.