Tachometer (REV Counter) reading 50% REVS

[Phenex]

My car since it has had a body off chassis refurb, is only registering 50% of the REVS i.e. what used to be 4000 RPM is only showing as 2000 RPM.

The car has a new battery and new cable from the alternator, but any ideas what could be causing this issue.
I posted on Facebook and got 100 AMP fuse, and some resistors but theses have been checked.

Cheers

Jay