coolant temp gauge & elec. thermoswitch

[Trevor Irwin]

(1989-1991 100/200)

The coolant temp gauge doesnt work, needle doesn't budge. It hasn't worked
since I've owned the car, but on a few occasions I have seen it work, but
this happens so rarely I don't know if it should be classified as
intermitant behavior.

I thought that the problem might be the electronic thermoswitch, which is
the older four terminal variety, but I don't know how to test the switch
itself.

I removed the connector from the switch and, with the ignition on, got 12
volts from the three contacts going to the temp gauge, A/C control unit,
and the overheat warning light. However, I only got about half a volt from
the plus voltage supply contact.

When I grounded the contact that goes to the temp gauge, I thought it
should have made the needle on the temp gauge go all the way up to
maximum, but nothing happened. Similarly, when I grounded the contact for
the overheat warning light and A/C control unit nothing happened (with the
engine running and the A/C on).

Any ideas?

Trevor