I am not familiar with the '50, but if they used the same assembly technique as in '55/'56, you will need to remove the trim surrounding the gauge housing/backing, which will expose screws that hold on the gauge housing/backing. Once those are removed, that will tip forward and allow limited access to the wires on the backside. Note, you will have to remove the speedometer cable from under the dash first before the housing or speedometer will come forward. If you have a factory shop/service manual, that also likely has some instructions for removing gauges.

I hope this is of some help to you.

Looking for suggestions on best way to remove instrument panel portion of dash. I need to replace some wiring to ampmeter, and other guages