What could cause my 1991 Mazda Miata to stall when the high beam lights are turned on or when the low beams are on and you engage the turn signal?

The stalling issue in your 1991 Mazda Miata when using the high beams or turn signals could be caused by an electrical system problem, such as a weak battery or faulty alternator not supplying enough power. Additionally, a short circuit or poor ground connection in the lighting circuit may be drawing too much current, leading to a stall. It's also possible that there could be an issue with the ignition system that is exacerbated by the increased load from the lights. A thorough inspection of the electrical system, including the battery, alternator, and wiring, is recommended.