K.. have a 93 Olds 98 that has error code for overvoltage to the ECM.. what would cause that? What you guys recommend troubleshooting? I'm thinking it could be phase burnt out on the alternator stuck on open.. but don't want to prematurely change it to find out.

Possibly the ECM itself. That'* the computer, right? My former H-Body was a 1989 Buick LeSabre and the SES light came once(I forget what code it was). The Buick(like my present Olds) did not come with any guages. A friend of mine had a Scan Tool and it showed the Alternator pumping out 19 Volts. He didn't think this was possible and surmised that it was probably the computer. Since you can't buy a computer and just return it if that does not solve the problem, we "borrowed" my mother-in-laws identicle 1989 LeSabre and swapped computers. Sure 'nuff, the same problem appeared in her car and mine was fine. I bought a new(rebuilt) computer and that was that. I'm sure there'* a better way to determine your prob, but this was my experience. Good Luck.

unfortunetly there'* no ECM from a same year.. but there'* a 89 nintey-eight just sitting there I'm thinkin they're both OBD-I and can both get codes pulled so swappin ECM from those 2 cars should tell if it'* the ECM or not right?

I once had an alternator that randomly put out too much voltage. You could see it on the gauge and also the lights were brighter. That is a possibility.