I;ve got an old Sears tuneup meter just like Paul WNC linked to. It works great on 4,6 and 8 cyl (has a selector) has a volt meter and dwell meter. It is also supposed to read amps and has a spearate hookup but I've never used that function.

I would really like to get my hands on an old Sun 1020 tester. The scope can help pinpoint all kinds of cyl ailments.