My wife drove the 1990 Miata home from work at night with no problems. This morning, the battery light stays on with the engine running and the headlights do not come on.

Notes: She did drive briefly through heavy rain. The engine starts normally. The headlights go up and down normally. Belt is correct torsion.

Any suggestions as to the problem?

 

Waterlogged relay?

 

That's possible. You are no doubt smarter than me when it comes to Miatas, so please can you suggest to me what to do, in layman terms?

 

It turned out to be a bad alternator, combined with a bad high/low beam switch. What were the chances of that?

 

Multiple problems at once can make things hard to diagnose. I'm glad you got it sorted.