Hey guys - I'm stumped. When I purchased my '68 Bird, it had a hood tach installed, but no harness to hook it up with. I purchased a harness, hooked it up, and all I got was lights. No rpm reading. I assumed that the tach was bad and purchased a reproduction one. Hooked that up, and all I get is lights again.

Here's how I have it hooked up:
Black wire to ground
Black w/ pink wire to negative side of coil
Gray wire to Acc Ign on interior fuse box

I have also tried to hook up the gray wire to the lamps receptacle on the fuse box.

What is wrong? Is there something wrong with my coil? Do I just have it hooked up wrong??????

That's exactly how mine is and it work's.
Sounds like you may have a bad tach. or a bad connection or something so obvious you're looking right past it.

I should mention that I have an MSD coil, but no "box".

You might want to check and see what MSD recommends either by the instructions or by calling them. The black with pink wire is the problem. You could have it hooked to the wrong side of the coil?
Jim