Taillights sometimes work, then they both go out, and come back

It's a simple circuit. Check ground. I don't know how that is done in a fish for sure. Get in there and look. If they have a common ground wire in the harness, maybe it is loose.

Otherwise, You have to get busy. The path is from the tail / park fuse, but that fuse also supplies the dash lights. Do they go out? If not, the light switch itself is likely OK. Might be the light switch harness connector, or the left kick panel connector. The passenger cars can get the harness pinched back where it enters the trunk near the back seat. Don't know about a Barracuda.