Temp & fuel gauges - what am I overlooking?

Put it back together. Heated up the old sender, plugged it in and grounded it, and the dash responded.

Reconnected the new one, ran a ground from the hex (body) to an intake bolt and confirmed continuity between the sender and battery.

I ran the engine with that extra ground connection to where the mech gauge read 160, and the dash gauge never moved. Ditto the fuel gauge. I guess I've got two failed senders, both new, at the same time. I'm skeptical but there it is.