my 88 seems to not want to turn on the rad fan, tried 3 known good fan switches, and none wana kick the fan on, turning on the AC will kick it on just fine, so, does anyone have a diagram so i can track down the problem? any common known things to look for?

thanks, just makes me more confused... i was hoping to see the AC bypassing the relay or something, but looks like the AC and the switch just engage the same relay... so why the F$#$@ are non of the switches i install working?! :/ guess i should check the wire itself.

The HVAC controls do turn on the cooling fan relay directly... this also turns on the AC compressor, now if the AC is dead, meaning no pressure, the fan will shut off as soon as you select a non-AC setting on the HVAC controls. But if your AC is working and you shut off the HVAC controls, the cooling fan stays active until the pressure in the system drops, then, if the coolant temp is low enough the fan will shut off...

Each one of these three paths is supplying a ground to the fan relay. My guess would be wiring, check your C500 for corrosion/loose connections as well.

[This message has been edited by carbon (edited 05-05-2014).]