1997 MC 3.1L Possible Electrical Issues - HELP!

I've had my Monte for 5 years, I'm the 2nd owner and the car was immaculate when I got it (22,000 miles, perfect body, perfect interior.) The previous owner was my aunt, who moved to Cali shortly after buying the car, and left it sitting in the garage for a few years. I do have a few issues that all seem to be linked to the electrical system (plus one that I know was my fault.)

1.) Since I got it, the fuel gauge has never worked. It will show full as soon as I fill it up, and just before I am about to run empty. All other times, it floats between F and E. (I've since had the fuel pump replaced, full setup, and the gauge worked for about a week before it messed up again.)

2.) My wiper fluid jets have never worked. Same fluid has been in the car since I got it.

3.) After a year or so, my sunroof stopped working. It has enough juice to get about halfway back, then slows until it finally dies. After a few days, it will have enough "charge" to get it closed again.

4.) A couple of months ago, my Cruise Control stopped working. The switch is in the stick along with the wiper fluid jets.

5.) This one was my fault. I added the NASCAR-style spoiler (w/ brake light) to my car, and when trying to splice the light to my 3rd brake light, none of my brake lights work now. Checked all fuses, all are good. Could I have tripped a breaker or something? If so, where would I find this?

Thanks for any reply!