Need help finding new temperature gauge

I finally had time today to get under the car, and I'm not having much luck with the wiring. The one thing I've verified is that the fuel sending unit is good (putting out about 80-ish ohms on a somewhat full tank). Beyond that, I'm not getting any continuity between the sending unit wire and the harness connector behind the driver kick panel. I also don't get any jump in the gas gauge if I ground the gauge-side harness connection. I can't see any reason for the lack of continuity between the sending unit wire and the front of the rear harness. Not sure of how better to test the wires - I've been had my ohmmeter connected to the sending unit wire and a wire from the harness connector long enough that i could connect both it and the sending unit wire together - nothing. I guess I could be having 2 problems, a bad wire and a bad gauge. At this point, I can't tell anything else.

How do I test the dash ground? It lights up with the headlights on, although the left turn signal indicator is dimly lit, and the turn signal indicators otherwise function normally. However, I can't seem to get either of the brake or oil idiot lights to come on. The moparfins article doesn't go into testing the dash ground, just says I might have a problem with it based on what I'm seeing.

Ideas?