It started

Car was 4pot 318is ( rpm gauge was rev happy on start up)
This wasn't my problem as I sourced 6pot 325 clock with correct plug in !
I replaced all cluster bulbs carefully one at a time avoiding any mix up , so they were nice and fresh

This is where my problem has started:
When the 4pot clocks were in place they read 1/2 tank of fuel
Plugged in 6 pot ( fresh ) clocks and they read jus a fraction under full tank of fuel !

Any ideas ?