i own a isuzu i-mark diesel. i was driving on the highway and the master warning light came on. i pulled over and checked anything i could see visually. i looked at all the grounds and i drained the water seperator. the funny thing is, is that the car doesnt act any different. it runs the same as it did before the warning light came on. i checked the owner's manual and the original i-mark workshop manual and neither of them have any information on the master warning light. Any help would be appreciated.

This could indicate the start of alternator failure. If the vacuum pump shaft seal leaks a little, the brushes start to disintegrate and the residue can build up on the internal regulator contacts. This can result in a rather dramatic upset of the electrical system. The raw unregulated AC (as high as 180v) from the alternator can get into the wiring system. My wipers (although not turned on) went faster than I have ever seen wipers go and stripped the plastic gear. The digital clock went off like a flashbulb as did other dash and panel lights before the fused link opened.
This was preceded by the master warning light and a week later voltage fluctuations especially after startup. And brief periods of no output from the alt. Good luck.