had battery, altenator and starter checked tested ok

With a 26 year old vehicle, all normal bets are off. The typical diagnosis would be a faulty voltage regulator perhaps, which should be an external unit on this vehicle. However, since you wait and it cranks again, I'm not entirely sure what other factors are involved here. Someone really needs to dig into the starting and charging system up and down to see what may be happening. The electrical ignition switch in the steering colum would be worth looking at, as they can overheat and cause shorts and such. A physical inspection could at least rule that out for an issue.