Common problem on the 83's. On my (and I believe most) car it was a bad connection at one of the main connectors behind the fuse panel. It over heats and quits making a good connection. I fixed mine about 20 years ago so don't remember exactly which one but it's about the 3rd one in working from pedal side towards exterior of vehicle. You have to remove the 1st and 2nd connectors to access the one you need. On mine it was obvious when I finally got to it. These connectors are square (or maybe rectangular) and have something like 3 rows of 3 pins although they don't use them all. I ended up running a new wire around the connector. I've posted this answer before but it's been many years.

Good Luck