Blower to highest setting lost power to several electrical circuits

Greetings,

After turning blower resistor to highest setting (4), I lost power to several electrical circuits ie: radio/blower, brake lights, interior lights &more
99 chevy lumina 3.1 - All fuses in all 3 fuse blocks are confirmed good.
My symptoms: The following are non-functioning: brake lights are out, power side-mirrors, ALL interior lights, radio, blower fan, cigarette lighter, ashtray courtesy lamp, hazard flashers; and the audible 'dinger' indicator.

Also, the auto door locks don't work (has been occurring since I bought it and according to the Haynes manual this could be a faulty relay or a broken wire in the wire harness sheath between the door and frame that is under constant moving when door is opened/closed), however after studying the wiring diagrams I realize that the auto-lock switch is also tied into many other circuits and I am starting to think that the myriad of circuits problems could be a single Ground connection loose.
Also (probably un-related) my driver side window has a short in it, because it only goes up when it wants to, and sometimes stops and starts again when I press the roll-UP button, most often making me press the roll-UP button, but thought I should tell you.

How I can duplicate the problem: This all started one day when I put the fan blower on to "4", the highest setting. The little I do know of electrical systems tells me that this is a variable resistor and that when on 4, the current is forced through the lowest resistance coil, allowing the maximum allowed current through, thus creating the highest-speed. When I turned it to 4 (hi) one night, everything went out. It came back on at some point temporarily, and then I duplicated the problem again when I put it on 4 (hi) again.

What could this mean? The only thing I know so far is that this could mean a loose ground wire (which would make sense). However, is there something else that comes to mind, now that you know this?
I know you cannot physically troubleshoot it, and only going by what I tell you, but just thought I'd ask.

Two last things you should know: I had a mechanic friend help me replace the wiring harness that goes between the car battery and the starter solenoid. I'm wondering if he put the new harness on correctly and if it is lose, however the first thing that came to mind when the problem first occurred was that I thought something had shorted out when I put it on 4.
The fan blower motor seems to work a little on 1 through 3 (low-mid) settings, however with very little power and basically only works on 3, although on 3 it is not as strong as it should be, but when I got to 4 the fan immediately shuts down and I hear the auto-door locks try to engage.

I already replaced the blower motor resistor and relay, to no avail, and the brake stop light switch. Within 20 mins of installing a new refurbished brake stop switch, all power to all the accessories I mentioned came back to life but lasted a week and I am back to square one. Replaced the brake stop switch again just to see, to no avail. All fuses are still good, however I have not tested the mini circuit breakers in the fuse bocks.
I realize I started in the middle of the circuit and should have started at the circuit breaker/fuse and traced it along but I had some guidance from a mechanic who could have sworn it was the blower motor resistor, and then told me to try swapping the brake stop switch.

I should have started to test for continuity but just bought a test light but unsure how to start, and was hoping it was a simple R&R. I understand that in lieu of swapping out the most obvious components that I should start at a ciruit breaker/fuse first and work backwards along the wire checking everything for voltage or continuity, but this is all so new to me, that I just haven't done it yet so I am sort of clueless, with an idea of where I need to be going. I am learning and this is all new to me however I have gone through 2 yrs of aircraft maintenance school and earned a avionics license elements 1, 3, 8 by the FCC. But have yet to get into the field and still a newbie, with everything to learn. I only know basics at this point, and unsure where to start.

Any thoughts? Thanks!