Tachometer Inoperative

[DCKane]

'87 300D
I'm new to the board but have been lurking for several months. Learned a lot (thanks) but not quite enough. Finally got around to replacing the black LCD OAT gauge. Figuring out the connection was trial & error. Replacements are 5-pin and mine was a 4-pin connector, but that's another story. The temp. gauge works great, looks great - but somehow I screwed up the tach.

I did not disconnect the battery (I needed it connected to see when the temp. gauge worked). Studying the wiring diagram shows the tach. circuit is always hot (I can understand the clock being hot but not the tach.). Checked all of the fuses (tach. is on 9). None were blown.

Pulled the instrument cluster back out to check all of the connections are tight (and the insulator didn't slip off the clock wire). Everything else on the car works perfect: climate control, lights, instrument lights, seats, etc. I didn't try the cruise control yet. Is anything else dependent on a functioning tach.?

The only other thing I can think of is the instrument cluster isn't grounded, however, everything else on it works. Is there another fuse I'm not aware of I might have blown? If I disconnect the battery do the relays all reset? Has anyone else experienced this? I read through back posts and saw discussed the OVP (but I couldn't find it). Your help solving this is greatly appreciated. Thank you.
dckane