I have one of those gauges mounted in my '74 Thing. It is actually a Westach gauge.http://www.thesamba.com/vw/forum/album_ ... _id=679730
It's probably 10 years old. I just went out to the garage to take a look at the back of it and here's what I found:
First, I was surprised to see that the tach doesn't require 12V power. Maybe I'm just blind. Your diagram seems to show +12V with ignition switched on connected to the terminal labeled #1.
I couldn't see a terminal labeled #1 on my gauge (that doesn't make sense to me) and I can't see it in your photo either.
Anyway, the terminal next to the light socket (labeled #5) is connected to ground.
The first terminal opposite the mounting bracket (labeled #4) is connected to the thermocouple black lead.
The next terminal (labeled #3) is connected to the thermocouple white lead.
The last terminal, almost opposite the light socket (labeled #2) is connected to terminal 1 of the ignition coil (with the green condenser wire).
The yellow loop is cut.
If the CHT gauge does not function, try reversing the black and white leads.
The thermocouple ring must be installed on a spark plug and no-place else. #3 is best.
I hope that was helpful, Mondshine