I just bought this new 98 civic LX manual. Everything is OEM. When I start, it runs fine but if I hit the gas pedal and rev it passed 2K RPM then all lighting inside and out starts dimming then comes back on sort of like flashing but it doesn't completely go out it just dim then come back on at a consistent rate. I thought it was the alternator and assumed that it might the regulator or something I have a known good alternator laying around and swap it but still does the same. Another thing is if I disconnect the ground battery then it would stop running even after alternator swap. If I turn it off then start it back up then run fine, but at anytime the rpm passed 2k then it does the same thing. I've never seen such thing before. HELP PLEASE.......................Thanks in advance.

 

The first thing I would do if I were you is call the previous owner and ask them what work had been done to the car. Was an amp or alarm system installed? Then just go down the list and look for wires that have been cut or damaged. A quick visual inspection of a lot of things could possibly help you source your problem.

Some things I would check

Fuseboxes, one could be partially installed or not pushed in all the way
T-stat ground
Tranny to frame ground
Valvecover to rad support ground

In my experience (which may not apply to all cars) I have found that if the alternator is good, you can disconnect the battery and the car will still run. Take your car to Oriley's or Autozone and have them run a basic test on the battery and alternator for free.

Good luck.