Is there a mod that gives an indicator of the enemies remaining health like Oblivion has?

The expansion packs.

This was added with Morrowind's first patch. You must be using a "first edition" Morrowind disc from May, 2002. If you patch your game or, as NaxoX9 says, install one of the expansions you'll see an enemy health bar.

OK, that's not what I'd have expected to hear.

I recently restarted playing this, and am patched all the way up to and including the MPP.

I don't ever get any enemy health bars. Where exactly do these appear?

It is the yellow bar that appears above your own health bar. You can see it when you attack an enemy.

D'oh.