I have a Nikon FE (30+ years old) It was functioning fine last time it was used about 15years ago. When I got it out to use this time I put a new battery in it but the light meter was only working intermittently, so i just used a stand alone light meter. I had a film i had half used in an Olympus and transferred it to the Nikon. When it came to developing the film the Olympus shots came out fine, but the Nikon ones were all fully exposed. What could the problem(s) be with the Nikon?
This camera has an electronically-controlled shutter, with a manual fallback to 1/90th of a second. See Why does my Nikon FE occasionally fire at ¹⁄₉₀th regardless of setting?.
It seems likely that with meter working only intermittently, the shutter is also erratic — possibly giving 1/90th, or possibly random values. Replacing the batteries and cleaning the contacts is a good first step, and if that doesn't fix it, either find a repair shop to do the whole maintenance thing — or put it back on the shelf.