Intermittent warning lights, temporary system failures

My 2000 Pontiac Grand Am GT1, with less than 70,000 miles, is beginning to act weird. On very rare occasions, maybe once a year beginning three years ago, warning lights will turn on while I’m driving, typically the “Fasten Seat Belts,” “Security” and “Service Car” lights. When I stop and re-start the car, the lights are out and it doesn’t happen again in many, many months. In April, it happened again but with a twist: the AC stopped cooling (the fan was OK)and the turn signals wouldn’t work. I got to my destination, stopped and restarted the engine, and everything returned to normal. Now, the turn signals have begun to malfunction on a more regular basis, with no warning lights on the dash. But they start up again. I’m retired and spending a lot of time in a small town in Central Mexico. Anybody have a clue what’s causing this? There is one good mechanic in town with computer diagnostic equipment. Should I wait until there’s a total failure to facilitate a diagnosis and repair, or have him experiment at extra cost? The car has been passing Texas’s annual safety inspections with flying colors – nothing shows up on their computer systems. Thanks mega.