1990 200tqw-overheating

[Ron Frazier]

I need some help trouble shooting an overheating problem. The coolant
warning light comes on as the temmperature of the coolant gets in the
vicinity of where or past where the fan should kick in.  I originally
thought it was the thermostat but I replace it and it didnot change.  I also
put in a new reservoir because it was slightly leaking.  I think the
overheating problem must be caused by the fan not coming on. I checked the
fuse box and it seemed ok.  Two summers ago I had a problem with the fan not
running when the AC was on.  I replaced the radiator thermo switch to
correct that problem.  I have yet to put 12v on the fan motor to see if it
is working.  I understand that there is a fan relay that is under the dash
that could be a problem.  Where is this thing?  Also there is a thermo
switch at the top hose connection to the head that sends the temp gauge data
and alarm to the  instrument panel and controls the fan?  Could this be part
of the problem eventhough it is sending the alarm and the temp gauge seems
to work as usual.  What are the other two sensors in this connection.  How
does this relate to the radiator thermo switch.  The aluminum strip fuse in
the fan wiring looks ok. Trouble shooting advice is requested.