Absolutely. Ford is cheap and if they could get away without having a working ECT, they would have done it.
Normally the ECT lives in the hot water feed tubes for the heater. Someone may have had a bad ECT and couldn't get the old one out, so they plugged the new one in and tied it up out of the way.
When you plug the ECT back in, dump the codes. Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.
See
http://www.troublecodes.net/Ford/
OR
See
http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See
http://www.mustangworks.com/articles/electronics/eec-iv_codes.html
IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
For those who are intimidated by all the wires & connections, see
http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.
If you get a code 21 when you dump the codes, the ECT is likely to be defective. Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error.