Thermostats and Temperature switches

[Lotusman]

I just put a No. 15 chip in my '89 non-SE. I am now getting a high temperature warning light whenever the temperature gauge gets to 80C. Never got this indication before. It goes off whenever I accelerate but comes back on when I drop the revs back. I replaced the coolant tank (quite rusty)when I changed out the coolant and flushed the system. And I replaced the level sensor. The sensor seems to work as after the car is started, the level check light goes out after a few seconds as it should if there is level there. Where does the signal for the dash warning light for high temperature come from? Is it the sensor at the thermostat housing or the one on the intake manifold heater? I am getting no check engine light.

Also, what is the expected life of the thermostat bellows and mechanism? I know I have lost one in a Honda after 14 years and a Taurus after 16. But I am not getting the back up of coolant into the expansion tank nor actual high temperatures as I did in those instances.

Lotusman
'89 non-SE