Aircooled VW South Africa

Hi Fellow Forum members.
I need some help with a VDO Gauge (REV counter) I inherited with my beetle.

1. How do I clean the glass without scratching it, any specific tips or is it just sunlight, water and elbow grease ? Btw, the glass does not look as bad, some dust on the inside most probably, the flash makes it appear worse than it is.
2. What is the safest way to open it without damaging it ?
3.I need to identify the gauge to get the connection diagram, or , I am sure this is quite easy, if someone could help with the connections to be made.
Obviously the 2,4,6,8 donates the number of cylinders, The beige adjustment screw to fine tune the rev counter ?
Top connector with the two pins is for the bulb, managed to pull it out, appears to be blown, where do I get a replacement bulb? How does this get wired up to the dashlights ?

The two thumbscrews I presume is for the mounting bracket.

Then we come to the interesting part (for me anyway, never seen the back of a rev counter before, yeah I know, office jockey), the 4 remaining pins in the middle,( with the bulb holder at the top). Bottom left is (-), (straight to ground I guess?) , Top left is +12V (connect this to a power distribution box in the front?), top right is +6v , (I presume you can use either 6v or 12v) and then the bottom right merely says 1. I am guessing you connect this to the coil somehow, or am I completely off base ?

There are a few numbered markings. Below the bottom right pin in the 4 pin cluster, it reads 830/3/4.
To the left of the bottom left pin in the 4 pin cluster it reads: 2.70

Above the left thumbscrew it reads: ZyL/4Takt
I cant figure out the blue writing, it looks like, massetrer/massefrei/massetrei/massefrel, just found one!, googled all the combinations, massefrei means something about mass free/insulated return - what on earth does that mean ?


Waiting with baited breath for your wisdom!
Thanks

No-one brave enough to assist ?

It looks like the tach fitted by the VWSA factory to the 1600SP Beetle. You need to carefully pry the ring around the glass away with a small, flat-tipped screwdriver on the inside, to seperate the glass from the rest of the gauge. Nothing cleans glass as good as normal Brasso and a soft cloth. If the glass is indeed scratched, I guess any home window supplier can cut you a new one, the hole in the centre might be a problem. There is some trick in connecting that specific gauge to the wires, I just don't know what it is. Normal rev counters are wired as follows:

Black wire - earth
Red wire - ignition positive
White wire - pickup (the minus terminal on the coil)
Green wire - instrument light

To clean the glass,Brasso,Vim and a lot of patience.

Just do a search This topic was done not to long ago think Impi or Callooker gave the pin outs and think it was obviously under Advice section

Thanks for the feedback gents!