Still can't figure out issue w/96 subaru losing power

Hi just repeating a problem that is still a puzzler for my mechanic – This winter my dashboard lights started conking out intermittently, but would always come on when I’d flip the headlights off and back on again. This happened randomly. Then two months ago after driving 75 miles, the speedometer and tackometer needles started going haywire, dancing around and then dropped to zero yet I didn’t lose power. Check engine and ABS indicators also came on. Two different mechanics ran diagnostics, one a day later and one several days later, but couldn’t determine problem. I took a 500 mile round trip in between problems. Then yesterday after it had been running great for two months following a tuneup, after I had driven 100 miles from home and was on the way back after a four hour meeting, the needles started jumping up and down and then went to zero. Drove another 45 miles before I completely lost power and had to be towed final 50 miles home. The next morning the mechanic said it started right up and he can’t tell problem right away, though still looking for answers. He keeps driving it and says it runs great, then lets it run while he works on other cars, but can’t replicate the problem I encountered. He thinks it’s probably not alternator after running diagnostics on it. What could it be? Can diagnostic tests miss problems? It runs great otherwise for short distances and intermittently for long distances. Thanks so much for any suggestions!

I would suspect the alternator causing this trouble. It may be putting out excessive AC ripple intermittently. That would cause the gauges to act like they did. The trouble may also be in the power buss to the gauges.

I am having same issue w/ my 98 Subaru – have replaced alternator FIVE times in last 7 months or so – originally mechanic thought the parts were defective, but last one was from a different supplier and only a month or so after installing, my car just died at a light this morning. Battery not drained, and mechanic was able to start it after had it towed there. What can it be???