If that doesn't do the trick for me, is there a way to disable just the
overtemp input to that circuit, and leave the coolant sensor working?

  I had that blinking light in my van from the day I bought it...the PO
couldn't get it to stop and neither could I...I messed with it for a while,
had the instrument panel out a few times trying to get it working
properly....then I took some black electrical tape and covered it up with a
nice neat little circle that I cut out and stuck right on the face of the
instrument....You can't even see it and that damn blinking light is
probably still blinking back there, but I don't give a ______!...  5yrs now
my tape has worked....70k very enjoyable hard miles on this van since I
have had it...

   Now all the Chicken Littles will chime in and tell you the sky will fall
if you try to drive without that blinking light functioning
properly....Whatever...I have better ways to spend my time than fiddling
around with teenie little wires and diagrams in a book in order to 'fix'
something I don't need anyhow.

  I check my coolant level when I head out on a significant drive.  I scan
my gauges as part of the task of operating the vehicle.  I have an oil
temperature gauge as well as a functional coolant temp gauge and the
alternator light will tell me if I've lost the waterpump belt....Screw that
silly little blinker.....
   Or, fix it somehow if you absolutely must....but I just blanked that
blinker-stinker right the heck out....