engine heats up quickly and burns spark plug wires???

I just installed a new thermostat to my 91 Ford Probe, but seems like back of the engine heats up abnormally and begins to burn my spark plug wiring. Is there something else that could be causing this? I was told it was more than likely the thermostat but even after the installation of the thermostat, the back area f the engine still gets hot and burns my spark plug wiring. I'm not sure if i just have to wait a little more time for the engine to cool down or what. I let the engine run for the 10 min to mix the coolant and still it burned. Any ideas?

did you put the t-stat in backward?

Not that I know of. I put it in the same way as the old one was in. Where the spring is facing the engine.

I watched the back spark plugs carefully and I noticed the smoke is only coming from the back middle spark plug. What could be causing that?

And I think I noticed that my coolant fan doesnt come on. Maybe Im not letting the engine run long enough, but from what I see it doesn't look like it comes on anymore.

could be a defect in the plug wiring if it is only that wire.. unless you have actually touched or know that it is the engine for sure.. besure it's not the one SP wire