I pulled out my switch to see why it was stuck. I found that if you are carefull not to lose the tiny pieces, it can be put back together.
After removing the switch from the dash you can dissassemble the housing. There was a tiny spring, a tiny plastic rod, and a copper/contact thing. These parts might be loose or just need a dab of grease. Otherwise, try to note their positions. Mine were loose and went flying...
The switch housing comes apart in two pieces, the switch side and the contact/connector side. I first put the spring into a hole in the switch side followed by the plastic rod on top of it. The rod must be seated just right to stay in place, and it will hold the spring.
Now on the contact/connector side of the housing the copper contact will fit. It should be obvious how it works and goes together, but mine wasnt. After three or four tries at what appeared to be the best fit, I decided to change its position to what looked close but not perfect. Seems that was it.
The copper contact rocks back and forth like a teeter-totter. It must be positioned just right to work. By small adjustments to its location -offset from what "looks right" -it worked.

Now the button will click ON and OFF....or does it ?

I havent figured out how it works. There is a timer, and I hear it clicking.
There are two lights on the switch. Should they both be off ? What does it mean if the square shaped light is on ?

I might disconnect the thing after all...

the switch passed the continuity tests on the bench..I think.

I can make both lights go out by flipping the button off and on. But when I start the truck again, the small square light is on.

I question my progress on this.

I'm assumning you switch doesn't lock in an on postion, which is normal.the 89 uses a timer for the defrost. use a test light or meter to see if you have power at the grid. one side is power and the other is ground. you can also hook to ground and touch the grid lines to see if they are intact or not.

I've got 5 monty/raiders currently and only one had a good grid. they might look ok but not have continuiuty acrross the glass.

I have a coulpe of switches if you need another.

Dave