My 1993 Mercury Tracer doesn't put out any heat and the temperature gauge stays on cold. I changed out my thermostat and nothing has changed. What else could it be?

I had the same problem with my daughters 93 Tracer today. I fixed it by going under the dash (on the drivers side). If you move the temp lever while looking at the parts on the heater, you'll probably see, as I did, that there''s a white plastic piece with a groove in it, that a little bent wire fits into. That wire accuates the temp control. Mine had come out. It has a little white attachment that fits behind the bottom (black plastic thingy) that holds the wire in place. I put a drop of superglue in it and put it back on. It now works fine! Hope that is your problem too. Good Luck!