electrical speedometer output signal to mechanical VDO GNX gauges

[paradigm]

I acquired a set of GNX style VDO gauges for my 87 GN.

The car is an LS swap car (I got it like that don't jump on me) with electric speed output, and I want the speed to display on the mechanical VDO speedometer. It looks as if the only way to do this is with a $400-500 convertor box.

That said does anyone know how difficult it is to remove the 3.5" mechanical speedometer and wire in a 3.5" GPS or electronic speedometer? What are the white and black terminals circled on the back of the speedometer for? Backlight?

Also has anyone trimmed a factory instrument cluster bezel to fit one of these? Any tips?

 

[TType85]

Black appears to be the light in the speedo. White may be ground. I replaced my mechanical vdo speedo with an electric one when it broke. Just had to wire it and set it correctly to the signal from what ever VSS you have. GPS speedo is probably even easier.

 

[Chuck Leeper]

A single wire light uses the base as the ground side.
Being the dash has plastic componentry; the white wire is there to assure the ground is complete.
A suggestion:
If you wire in an electric gauge, do yourself a favor, and do away with those nasty crimp terminals.
If you have the terminals, pull the plastic off, use a terminal sized for the wire gauge, a good quality shrink tube, and the proper crimper tool.