Thanks Jeremy, that's exactly what I ended up doing.
I do have that 2nd pin in the cluster though...
To formally end my tach mini-saga: It was a simple missing ground issue that was traced to a broken PCB path due to a "positive", in my case the clock connector, making contact with the metal backplate of the tach cluster. Fix was as simple as fixing the looped end of a wire to PIN 1 (12 o'clock position) and sandwiching the other end to the metal "bridge" strip.
btw... i tested the tach gauge when it was still separate from the rest of the cluster by attaching it to its connector and grounding the metal backplate to chassis ground. This should've been my first step, could've saved me a lot of time and frustration.
oh well
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85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project