Strange dash cluster problem

[R3cK]

hey,

got a strange problem with my gauge cluster, thought it was broken so put in a new one but got the same issues..

positive:
-watertemp works
-distance counter works

negative:
-rev jumps one time when i turn the key and stay at zero then
-speed vibrates at zero
-fuel doestn work at all
- by braking the left turn signal turns on in the dash (but my light is broken, but should be on anyways i guess)

solutions?
-new cluster --> same issues
- ... ?

Where should i start? The signals are all independet:
Fuel --> pump ,
speed --> gearbox,
rev --> ecu


DAFUQ?

[R3cK]

it has to be some ground problem.
can anyone help me how to locate this?
where should i start and how to measure right? any tactics by looking for wrong ground?

please guys im lost in this electronic shit