I thought I would post this in case anyone else may have a similar problem.

My heater switch is a three speed. At first one speed failed, then the second speed failed until I only had high (noisy) speed. I removed the center bezel thinking it was the switch. It was not. I expected to see some sort of resistors in the switch that I could replace or just replace the switch.

As it turns out the resistors are behind the glove box installed in the cool air plenum. I removed the resistors (two screws) and you couldn't tell anything was wrong with it, no burnt areas or any indication of failure. I purchased another one from my local ford dealer for $39 bucks taking a chance that that was the problem. It was the problem, my heater now has 3 speeds as before and I am relieved. Not all my repairs end up this easy. Bob F.