1986 BMW 325 speedometer

Electrical problem
1986 BMW 325 6 cyl Two Wheel Drive Automatic

Gents,

I have a bmw 325E 1986 my speedometer does not work on my car, I tried to replaced at least 5 same unit from pick your own part but same result. I am convinced that it's not the unit could be electrical, I am new to bwm toy can anyone help?

Thanks,
Chris