Have them take a look at the exciter wire. That is, the small gage wire going to the alternator out of the harness. I had a situation once where the car was running great while driving in decent rain that was falling right after a big wet snow. There was a lot of slop getting thru between the engine bay pan and the wheel arches being thrown into the engine bay. Then there was the slop being picked up by other cars that was making it thru the rad. The engine bay was soaked as much as if you were doing an engine clean plus the engine was running just that bit hot because of the grille being blocked with slop. Anyway, I stopped for coffee and after that it wouldn't start, or spin for that matter, displaying all the signs of a dead battery. Went to the Can Tire that was right there and they came out with the load tester. That told me that both the battery and alternator were bad. While the tech was doing his thing, I noticed that the whole back of the alternator was soaked and the exciter wire connector was half there. I reached in gave the wire a wiggle and the test starting showing good results for both battery and alternator. I gave the wire another good shove and started the car fine. Got the thing out of there, made it to the stop we were trying to get to along with some other stops, all being fine. Put a end terminal on the exciter wire and never had a problem after that.

Any road, just a suggestion.

Cheers,

Bill