VDO tach doesn't work, only 2.5 volts

[GNRick]

The tach started getting flaky, then quit working all together. It is a VDO. I have a black wire, red wire, and white wire. Black is ground and red shows 13 volts. White only shows 2.5 volts. Is this how it should be or has the white wire gone bad? I think this happened once before and my mechanic spliced in a new white wire. I can't believe his wire has gone bad in 5 years. Or maybe the original white wire developed another bad spot closer to the ignition module? Thanks.

 

[Lil Truck]

I had to add the Caspers signal converter to get mine working. Do you have one installed?
Also if you changed out the ignition module some do not support the tach output.

 

[GNRick]

I recently installed a new module with one from Advance but never had a problem with them before. I'm pretty sure the tach starting failing before that, though. Or is it the white wire started going bad?

 

[TurboBuRick]

Like mentioned it sounds like the signal converter. Caspers has them.

 

[GNRick]

I reinstalled the old ig. module and now get 6.75 volts on the white wire. The original VDO tach still doesn't work so I know it crapped out. I tried installing the new tach (which I bought 4 years ago) but it reads 100 rpm at idle. Does this mean I need Casper's signal booster? I emailed VDO to see what they will say. Seems like they should make the proper gauges to work in our cars....or maybe I'm just in a bad mood. BTW, the old ignition module was a Wells and the new one is a BWD. So do all BWD's not send a proper tach signal? The BWD was only giving me 2.5 volts. Or would it not matter if I had Casper's signal booster?

 

[Lil Truck]

I have 2 GM modules 1 original 1 new from nos for GM. They both work with the Caspers tach module, I tried a new BWD it did not work. I have heard VDO will modify the tach for free if you contact them. I just bought the Caspers.

 

[GNRick]

The instructions for the dip switches are incorrect, I found out. Or maybe I should have been looking at the alternator chart on the bottom of the instructions. Correct positions are up down up. Tach works fine now. I even fine tuned it with the potentiometer screw. http://www.springfieldstreetrod.com/newimag/VDO_DIAGRAM_C.jpg

 

[Williams3982]

I have the stock guages and my tach isnt working either , everything else is so maybe i should start here...thx for the posting so i have somewhere to start looking lol


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[GNRick]

If you haven't changed the ignition module then you will probably have to contact Caspers for the repair.