OK, I cleaned up the schematics, first of a re-work of 'fatmobile's' 91 golf gasser tacho schematic...
I'm really unsure about this one, there are a few bits that seem odd, possibly incorrect? It seems too far removed from the 83 version and the TD version to be right?
Now we have the 85 TD Jetta...
The line from pin 7 coupled to groung via C1 is causing me concern...
My 1983 GTI gasser tacho...- notice the similarities with the 85 TD tacho...
I'm 100% sure on this except 1 resistor value (R5) because this has been removed by me during previous modification.
Modified 83 GTI tacho as per instructions from 4crawler link mentioned above
Notice that it is starting to replicate the TD schematic but misses crucial capacitor changes.
The load resistor R8 limits the needle swing, I intend to keep full needle swing and modify the tacho face so that 5000 rpm is now where 7000 is - I have some nice template files to create your own custom dials if anyone is interested?
If I make a small change to the TD schematic (added red line it would now match the layout of the gasser schematic, could this line have been missed on your original sketch?