I had a series of non-related electrical problems with a 4 wheeler about 30 years ago .
When I started the car, the left turn directional would come on at about half brightness without the turn directional selected, the left head light would be at half brightness, the windshield wiper would come on at slow speed even though I hadn't turned it on, the windshield washer fluid low level warning would come on .
Luckily I had the manufacturers shop manual with the wiring diagram, I traced it down to all of the effected circuits had the same ground or earthing point .
I found the ground/earth corroded where the terminal end was bolted to the frame/uni-body .
Anytime I hear of multiple electrical problems, my first thought is to go to all of the grounds/earths and check them for corrosion or looseness .