Electrical probs have eluded diagnosis - 5-SPD EX

The first symptom - five years ago - was the digital radio hopping frequency when it was very hot and humid. I figured that a wire was exposed somewhere, but the garage advised that everything was in order and that I must be hitting the radio dial inadvertantly. Hmmm. Anyway, it just so happened that I was on the road a couple days after that useful insight, and travel that day was very warm but dry. I had the ac on and cd playing and was cruising along at 65 mph on the highway, when most if not all of the dashboard lights lit up. Oil pressure was fine, engine was not overheating, gas was fine. Fluids had all been checked at the garage the couple days before. I turned off all unnecessary items, and reached my destination, however, when I tried to turn the car on 30 minutes later, it was dead. Had AAA come and jump it. I ran it for awhile and it remained charged through the weekend, and I was able to travel home without incident, though I chose to not run the AC, etc on the ridge home. Took it to the same garage and they could find nothing. Battery was fine. They did change the alternator, though, since it was under warranty, but neither they nor I thought it was going to solve the issue.

Last year, similar situation: hot day long trip, arrived at destination, visited with friends, went back out to car a few minutes later and it was dead.

Recently, yellow check engine light has come on intermittently, but garages (two) haven't been able to figure out what is going on. One garage was able to identify code p1259, but said that it was a red herring. And - the cruise control is cutting out occasionally on the highway. Sometimes it will allow me to set it again immediately; other times, I just drive without it.

BTW - the same garage that told me I was hitting the radio dial and not knowing it also advised that the yellow light on the dash was on because I needed more oil (I though the red oil lamp was for that?) And that was what was causing the cruise control to cut out. However, since the oil change a few days ago, the cruise control is still cutting out.