Absolute electrical failure in '97 SL4

My wife's SL will randomly lose all electrical power, including blinkers, starter, headlights, horn, door locks wipers, everything. battery seems ok when tested...sometimes it happens while driving. Other times, it will be running fine, shut it off, then nothing. After a while, power comes back. What's the deal? Not much of an auto-head yet. Need help. Thanks!

if it is a intermiddent problem, then chances are it is a bad connection. and i bet to have a AC delco battery. check the positive terminal, bet you its got a ton of crud on it. try cleaning it with a water/baking soda mix and a brush(keep in mind that is battery acid, so wear gloves, safety glasses, and a old shirt). if that doesn't help, you may need to replace the battery and positive cable or you may have another problem.