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I just recently bought a 1997 honda civic, and it works fine except for an electrical issue. The dash lights randomly dim, along with the headlights and the dash fan. I've tested the 3 times. I put in a new computer and reset it. Nothing has changed. When the engine is cold, it doesn't happen.

 
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It could be normal and you aren't used to how Hondas work.

Click this PDF article (LINK) and learn how this charging system works and why you can see wide variations in voltage compared to other brands of cars.

Monitor your cars voltage while driving around.....Note what your system voltage is when everything looks normal, and note again what the voltage is when you say the lights look dim.

It's normal to sometimes see less than 12v while driving around. Yes you can see the lights change and the fan speeds up or slows down.

 
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I'm assuming this is happening while you are driving and the engine is at operating temp...typically when the fans kick on it draws a bit of energy causing a fluctuation in the rest of the system...which would explain why it doesn't do it while the engine is cold....anytime I turn anything on an item that requires electrical power...ie...headlights and blinkers....my dash lights dim for a split second then return to normal...something I am used to after driving multiple different Hondas

 
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I have a honda ridgeline and it doesn't do this at all, however, it is newer than my civic. I've tried monitoring the voltage when the car is warmed up and idling, but ill try when it's driving.

 
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Will there be enough of a fluctuation on the gauge between 12.4v to 14.9v (lowest to highest stated in the PDF) to really be able to tell a difference for the slight moment the lights dim...

Something to look for is anything that may have been modified in the electrical system...before cars came with decent stock radios it was popular to swap all this out and add subs and amps and the like. even if the car doesn't have aftermarket stereo in it right now...it doesn't mean that it never did and the hack wiring job is causing issues now...just something to keep in mind.

I know I've messed up a fuse or two playing with speakers

 
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Depends on how perceptive the driver is.



Honda even issued service information because so many people notice lights get dim and bright as the system changes charging voltages:
Please read this PDF
http://www.skidmore.edu/~pdwyer/e/fi...lights_eld.pdf




Voltage can drop under 12v in low mode and it's still ok.

 
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some stuff may still be modified and might still have a higher draw on power...aftermarket radios...door speakers...if the prior owner went through the trouble of putting dynomat in then most likely some of the other stuff got modified too...when all the aftermarket got taken out he/she probably didnt bother returning it completely baack to stock wiring...stuff like that can cause it....especially when everything else that is suposed to kick on does.