VDO Guages setup on 88 Merc 115

[Diamond Chad]

I am chasing down the reason my Tach on the CVX 16 is non-functional.  So far, a visual inspection from the Tach and following the grey wire back to the connector into the control unit, and re-seating that connector is all the father I have got.  I will get out the multi meter next, but aside from +12 across the purple and black power supply wires, I'm not sure what to do with it.

Anyone with this setup tell me, when you turn the key on, do you see a little bump in the tach needle, indicating a sign of life?  Mine sits dead still.

Where do chase it , if I get continuity from the control center connector grey to the back of the tach?  (which I suspect I will)

Thanks

[Rich_V174SS]

The purple wire comes from the key switch and is +12 when you turn the key on, black is negative ground to the battery. The grey wire goes from the engine's rectifier or voltage regulator directly to the gauge. First verify that you have +12 and ground at the terminals on the gauge using a test light. If you have power the gauge needle should return to zero. Check continuity on the grey wire from gauge to engine, if good it's possible the rectifier or regulator is bad if not the gauge.

[Rosscoe]

I had to replace my tach this year for some unknown reason.
Now my trim gauge don't work

[Plugcheck]

Most vdo tachs have several dip switches on the back to set operation.  Couple are used for number of cylinders selection, and a couple are used for if the tach is being driven by a pulse source like a stator.  My $0.02, Michael.

[Diamond Chad]

Thanks a lot, got it,  will report back the results.

[Plugcheck]

     I found my instructions for VDO programmable tachs, let me know and I will scan it and post it for ya if ya cant find it online.  Off the top of my head, there are three switches, the first one on is for coils, 1 switch off is for alternators.  switch 2 and 3 set  the number of cylinders/pulses.   Check with my tachs in the show cars, and they are the same way, those tachs date back into the 80's

[Diamond Chad]

As expected , I have +12 across the purple/black power and ground, and continuity from the grey on the gauge to the grey on the control unit plug.

Next what it the approximate location where the grey wire is exposed under the hood, to make sure I have continuity from the motor source to the grey at the control box?

If that's good, must be the tach itself.

[Rich_V174SS]

The grey wire connects to the voltage regulator (or rectifier) on the engine.