Whelp. Tach had no hanging wires.
Tail between legs i buttoned it all up and now the sender works.
Car just wanted that sort of attention.
I did notice the diaphram on sender is a bit loose. Maybe i should have put some solder in that joint for ground. Or maybe it needed a bike pump pressure test to crack it loose inside.
Something tells me ill be visiting this again.
Cheers.