Unplug the plug in the sender in the radiator (on my '84 its on the driver's
side of the van).  Then just get a small piece of wire and jumper the plug
(put the bare ends of the wire into the holes in the plug).  The fan should
start right up if the relays and fan are getting power and are OK.  If the fan
comes on then you know that the sender in the radiator is at fault.  If
nothing happens then check the fuses, relay and get some juice directly to the
fan to see if the motor is burnt out.
Have fun sharpening those troubleshooting skills.
Ken Wilford
John 3:16