Puzzled by electrical symptoms...pls help solve

[TweetyDee]

I have a 1990 Corolla and have loved all 197,770 miles of it. Last week, while driving on the freeway at 3a.m., my brake light and battery light both came on, flashed, then stayed on. Half way through the next day it turned off and stayed off. I chalked it up to the heavy rains we have had lately, thinking something may have gotten wet. I didn't give it a second thought until they came back on last night. I also noticed last night that my guage
backlights were periodically dimming for short periods of time. To top it all off, this morning, after the car warmed up and I was on the freeway, the stereo joined the odd behavior club. When I had to take my foot off the gas,
the display would start blinking and when I dropped down below 30-35, the display completely disappeared. The battery is fairly new, new starter, and I have never had this reaction from a defective alternator. Does anybody have any ideas?? ***the stereo is a Sony Xplod. (5 yrs. ago, a co-worker of mine bought a Sony Xplod and had major electrical problems soon after)
I REALLY WOULD APPRECIATE ANY INPUT......THANK YOU!!

[lws6772]

I would start with a visual inspection of the wiring, check ground connections and check for loose connections(like on the starter). Make sure and look for any wires that might have a bare spot that is shorting to ground or maybe trying to ground through an adjacent wire. Double check any new accessories that might have wiring problems.

[joykill]

might be the alternator