Well, I just got my tach working too. It also was corrosion in the EGR Control Module connector. I pulled off the socket and nasty greenish white water came out! You can see the mess on the door sill in one of the pictures. I think the water in mine came from a cracked hose for the AC drain.

I blew all the water out of the connections with a compressor, cleaned up the pins with a bit of fine sandpaper, blew clean again, applied a bunch of dielectric grease, reconnected the module, and voila - working tach. Now I just need to repair the crack in the little hose.

Sorry, I didn't think to count the little connectors in the harness before I filled it with grease, now I can't really tell which holes have connectors in them. My best guess is that they matched the circuit diagram above.

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