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Radiator Fan won't stop

1986 4kq radiator fan continued running for hours after engine shut down
last night. To save the battery from total depletion, I disconnected power
to the radiator fan and went to bed.

Now, on Memorial Day morning, I need to diagnose the cause and get started
on fixing it.

Bentley shows radiator fan operation is controlled by a thermoswitch in the
lower left corner of the radiator.

Can I assume that the thermoswitch is stuck in the zero ohm (FAN
ON)position, or is it possible that there is a relay somewhere that is
stuck in the (FAN ON) position?  Or some third unknown control that I don't
know about, such as a tie-in with the air conditioning system?

It seems reasonable to reconnect the battery, allow the radiator fan to
run, and then disconnect the wire from the thermoswitch and see if the fan
stops running.

If it stops, then I have a faulty thermoswitch. If it continues, then I
have a faulty relay OR there is another circuit running the fan.

Well, its raining lightly outside and I have no garage, so I am writing the
list to see if I am on the right track, rather than going out and getting
all wet trying out my reasoning. This way I can be all wet electronically.

I'm sure at least three people have BTDT, and can help me along.
Incidently, I have a 1982 VW Jetta diesel parts car in the backyard, and I
suspect that it has a good thermoswitch and a good fan relay, in case
anyone knows of the interchangeability of such parts. All the parts stores
are closed today in my locality. 

TIA,    Doyt Echelberger    1986 4kq