Coolant Fan sensor in 87 4kq

[Cade Carvell]

Hello,
  Long story short...I overfilled (I think) my coolant expansion tank
last week...Which then caused the expasion tank to crack and the cap to
go bad.
  Today I replaced those parts and started the car again.  The temp kept
rising and the fan didn't turn on.  So I did the checks:
   1)  Fan works with a 12V battery feed just fine.
   2)  Relay tests good. 12V causes it to Kick (Click)
   3)  Checked the Lower radiator sensor measures .6 ohm resistace.

Questions:
   Since the lower sensor records .6 ohms, should I replace it.  The
Bentley states 0 ohm resistance when open (Up to temp and fan should
turn on).  I also noticed that if I go under car and short across the
connector to wiring harness - Lower radiator sensor (0 ohm it) the fan
still doesn't turn on with key off.
   Did I miss something?  Is thier a fuse somewhere that controls this?
Is thier another sensor?  I recently replaced the lower coolant neck
sensor (Looked bad :-) ).  It worked after that (2 months ago)...DO I
have a common wiring harness problem here?  If so, were would be the
likely spot?  Any other tests I should run?

Thanks to anybody with an idea or help, the poor Audi is grounded till I
get this one narrowed down. :-(

Thanks,


Cade Carvell
National Business Systems, Inc.
2919 West Service Road
Eagan, MN 55121
Office: 651-994-4400