Sounds like it could be a battery charge issue, if the battery is not a sealed type, remove the caps and check the electrolyte level in each dell, if it's low add distilled water only, I would charge the battery then, and also check the cables at the battery for security and corrosion.
Also follow the negative cable to where it is bolted to the transmission, again check for security, and corrosion.
Welcome to the world of 25 year old motor vehicles !!