S.O.S. blower fan blow out?

What would cause my blower motor to go from blowing high(4) to blowing as if it was on low(1) without changing the Blower settings?
There's days it'll blow like it should on high consistently and some days it'll start out blowing hard and it'll all the sudden barely blow at all. Other days I turn it on high and it only barely blows period from the get go.
6 months ago, I changed the ignition switch and the black/yellow wire leading to my heater had either a)caught fire at the switch or b) came extremely close to catching fire.
Either way, after I changed the switch, the blower finally started working (hadn't worked period for almost 2 years til I changed the switch)
Now it's doing this. Wtf?
Anyone ever had this issue?
Any ideas?
<---is by far not an electrician.

I've got this problem too, can't help you though cuz I haven't taken the time to check it out though mine started last winter, all summer my blower worked fine now its acting up again. Also my power windows and door locks only work when they want but only one one at a time. ( All windows come and go at the same time) I think I got the winders figured out though

If you have a multi meter pull out the switch unplug it, looking at the plug on the switch, with the clip on the bottom. Check for continuity across all of the top terminals. Switch to speed 2, now u should have continuity across the 2 outside top and the bottom right, 3 top outside 2 and bottom middle. And high should be the top outside 2 and the bottom left. And with the switch in the off pos none of them should have continuity.

The fan resistor on the bottom of the blower assembly may be the cause. The factory manual describes how to test it. A spare should be nearly free at a salvage yard.