I've been having this strange issue with my 2002 wrx with 108,000 miles on it. I've searched forums and extensively and I can't find anything similar. This will be a bit long, but I want to give the full background and not leave anything out.
About 4 months ago or so I installed a set of cheap ebay HIDs that I had laying around from another car. Since they were the right bulb size, I installed them and the wire harness with a fuse. At idle, they would flicker and it annoyed me, but I put up with it. I heard screeching from a bad pulley or something, did some research and decided it was either the AC idler pulley or alternator. I guessed alternator because of the lights flickering so I replaced it. I started up the car and found out it was the AC idler pulley and the HIDs still flickered. I just cut belt the belt off the AC side to get rid of the noise. It was an old belt and it was winter.
About a month and a half ago I was driving my car home from somewhere at 2AM and everything electrical went crazy. The only mod to the car was a set of HIDs. The dash lights kept dimming and getting really bright, my head lights kept flicking on and off and they got brighter or dimmer, the guauges started not working and going to zero and then coming back on, my ABS light came on and the radio shut itself off. After about 15 minutes or so of everything going crazy, my car stalled. The car would not start. The windows went up and down very slowly and everything like my hazards were dim. These were normal 100 mile round trip drives that I made weekly for about 4 months and never had a problem. I got my car towed by AAA to a local shop. They called and said they drove my car around all day, literally, and didn't have any issues.
I went to pick my car up and went to get in with just the key and the alarm went off. The alarm hasn't worked since I bought the car in March of 2010, but now it does. When I use the keyless entry, the lights now flash upon locking and unlocking, which has never happened before. I had a cheap flex innovations ground kit that I bought awhile back and installed it. The car idle is much smoother, but the HIDs still flicker. I took the HIDs out and went back to normal halogens. My car has been fine since. I haven't been doing the 50 mile drives as much, but I've driven about 4 of them since then with no problem.
Fast forward to yesterday, my car does the same thing it did previously, gauges go on and off, ABS light comes on, headlights turn on and off, the dash lights dim and flicker between various levels of brightness, the radio goes off and I also noticed that the wipers go really slow. The car stalled about 48 miles into my 50 mile drive after doing its strange electrical stuff for about 10 miles. The car wouldn't start, but this time, I turned everything electrical in the car to off and let it sit for about 5 minutes. It started right back up and still acted strange, but I got to my destination. I drove home that same night and had the same thing happen 40 miles into the drive. This time the car only acted strange, but didn't stall. One thing I noticed was the temperature gauge seemed to be lower than usual when the car acted weird. It would be at the bottom end of the normal temperature range instead of right in the middle like usual. This was something I noticed while having the problem, so that could be related to everything just going out. When the car acts normal, the temperature is normale.
This morning I drove the car to work, about 15 miles from my house, with no issues at all and it starts right up.
Any idea what could be causing this or any ideas on things I could inspect to try to get rid of this issue? Any suggestions will be greatly appreciated!
As a side note, I've gotten CELs for misfires in cylinders 1&3. They go away on their own and show up again like a month and a half later. I ordered NGK plugs, just haven't had them installed yet. I'm still trying to decide if I should try it myself or pay someone to do them because it's way different than Honda spark plugs that I've done in the past.