mk2 instrument cluster circuitry for tach

[jb86]

car started as 91 eco diesel.
stripped it all down for paint last winter and put in new engine - 1.6l hydraulic head, K24 and giles modded IP with LDA boost.
looking to ad a tach.
the "W" terminal tach clusters as i know were only in canada.
i googled vw diesel tach and found the crawler 4x4 article on the optic sensor.
he has a MK1, the cluster is different, theres a mounting point on the rear to connect to the tach.
the MK2 doesnt.
i have the cluster with clock from my 91 eco diesel and a second from the (identical 91 eco diesel) parts car and a gas version cluster with tach - same single plug as mine.
besides the issue with the cluster, my plans are to use an inductive proximity sensor facing the cam sprocket (counting 6 openings in the face) instead of optic sensor. i just have to work out the circuitry - this way there is no disc glued or bolted to the IP that could cause balance issues or fly off.
>>>>what im looking for right now is where to find the wire that operates the tach on the cluster.

I found by comparing the back side of both the tach cluster and non tach cluster that there is one single connection in the Mylar that is on the tach version and not the non tach version
Looking at the back of the cluster, along the top at the left corner is a Phillips screw, then 2 crimped connections to the Mylar, a small space, 3 crimps, small space and a single crimp connection
The last is not on the non tach diesel cluster
I plugged in the loose wire harness and touched each wire with a continuity tester and also the single crimp connection
I got a clean continuity on a red wire (the only solid color red wire)
I got a phantom illumination on the black and 1 of the 2 dark blue wires

I compared the wiring schematic in bentley between the German built diesel 1991 and German built gas (not 16v) 1991

There is no specific (that I understand) for wiring inside the cluster
But
1 thing I did notice- the 1990 jetta diesel/1990-1992 golf diesel version on (page 196) shows the tach as G5 and a .35mm (22ga) red wire leads up to it (kind of)

P. 207 gas not 16v German built 1991-1992 jetta
Shows a red .35mm coming from line "j" toward the tach and a green .35mm leading away from it on the right ending at "83" in a box (ground?)

Then whats weird is the diesel 1991-1992 is opposite
Line "w" leads to the green .35mm to the tach and the red .35mm leads away from it to a square box "87", but that red doesn't seem to line up near the tach anyway
jon

[regcheeseman]

Pm me your email - I'll send you a diagram.

[92EcoDiesel Jetta]

I did what you are trying to do, put in a CE2 gasser tach into an Ecodiesel. It's been working great, but much later I found out that my dynamic high oil pressure alarm does not work anymore since the cluster is not getting the W terminal signal from the alternator. It'd be much nicer if you can find a Canadian CE2 tach that works off the W-terminal so you also have the high oil pressure alarm.

[jb86]

Alternator has the large gauge wire going to starter
And 2 small gauge wires - a red and blue. Those attach to a plug near the battery location
Is either of those the "w" terminal?
Jon

[92EcoDiesel Jetta]

Alternator has the large gauge wire going to starter
And 2 small gauge wires - a red and blue. Those attach to a plug near the battery location
Is either of those the "w" terminal?
Jon

yes

[regcheeseman]

Blue is alt excite D+
red is W terminal

[vegged-out]

Can anyone tell me which pins are which on the back of the mark 2 diesel tach? There are 3 pins in a 4 slot plug.
Looking at the back from left to right there is pin 1, space, pin 2, pin 3.
I have mounted the tach in my Vanagon cluster but will have to hard wire the pos, ground, and w terminal as the gasser foil was wrecked at the tach plug-in.
Michiel