A few weeks ago I removed the heater core from my 1991 f150, and now I can't remember where this cover belongs. I'm assuming it belongs under the dash, but I've been changing lots of things. I'm sure you guys will have the answer.

 

pic of my 95 under there, may not help, what does other side look like on yours

 

Nope, sorry turns out it covers the throttle body. I didn't take it off after all, but it was in the cab, so...

Just took a 60 mile round trip. Turns out I definitely need to work on the brakes because the fronts seem to be doing all the work. There is also some power issues with the clatter, but for the most part it's a driver.