'89 740 107k Miles

I read a bunch of posts on jumpy speedos in a Search, but mine does not jump when sitting still like most.

It acts exactly like a sticky speedo cable of years past, being perfectly smooth for a few moments, then jumps around before settling back. It always returns and stays at zero when stopped.

The car was not used for a couple of years, and back then it was perfect, but started acting funky when re-activated recently.

I guess the connector junction box in the sedan is inside a black plastic box under the carpet at the left wheel well? I think I saw it there when I had the carpet pulled back recently right next to the radio antenna motor?

And the sender is inside the differential (which side-is it hard to find)?

Also I guess it could be a loose connection at the instrument cluster itself?

Just trying to get my "Ducks in a Row" before attacking the problem, and having a game plan.

Any other suggestions?

Thanks-
Bob