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914World.com _ 914World Garage _ tach testing

Posted by: Alphaogre May 30 2015, 05:27 PM

I am in the process of trying to get my tach working. I baught a used one under the assumption that mine had an internal issue. The second used one I picked up also is not working when I hooked it all up.

I read on an old pelican forum that you can test the tach by connecting it outside of the wiering harness by connecting the + to Power the - to ground and the blk/purple plug directly to the - on the coil. Would this infact work? What if you dont have the original coil, but a replacement one? would that matter?

I connected the + of the tach to the + on the batt, then the - of the tach to the - on the batt. I then connected the blk/purple connector directly to the - on the coil. Am I doing somethint wrong here?

Are these VDO Tach known for going out? Any help would be great! This is all on a 1970 914 4 1.7

Posted by: Spoke May 30 2015, 06:31 PM

Connecting blk/purple to NEG on the coil is how it is connected in the car. By doing this test you are taking the wiring out of the equation. Good way to test the tach. I doubt both tachs are bad. You may have a wiring issue.

When was the last time your tach was working?

Posted by: 72wrxporsche914 May 30 2015, 11:38 PM

The tack also needs 12 volts . Check your power with the key on .

Posted by: Alphaogre May 30 2015, 11:50 PM

I checked it while it was running and the tach was getting 12V. Still perplexed...

The tach stopped working right as I bought the car, right before I stripped and restored it. That's why I wanted to see if they would work directly powered. It is also why I bought the second tach, I assumed that the original had internal issues but never really tried to chase down the issei until today.

I wanted to test the tach's to be sure they were working before I go chasing wires all over the car.

Posted by: 72914wrx May 31 2015, 12:29 AM

Use a volt meter and Omh it out the wire form the tack to coil . Should be at 0.2 to 0.3 .

Posted by: timothy_nd28 May 31 2015, 07:52 AM

Send them to me, I'll test both of them for free.