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sprite tachometer

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VictorVictor

VictorVictor

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I recently took off the tachometer from my 65 sprite because it didn't work at all and are now trying to figure out how this DAM thing works. The question i have is how do electrical tachometers work (its princepal), how does it get the information of the RPM's, if it only has a white wire that loops through it with out making contact, a green wire that goes to the flasher unit and ground. Can anyone explain. Thank's for looking.

P.S. I don't know diddly squat about these cars. /ubbthreads/images/graemlins/hammer.gif
 
Basically, the white wire loops through a pickup on the tach where it is inductively coupled to the tach electrics. The white wire feeds the ignition in short current pulses as the points open & close. The tach counts these pulses & converts the information to rpm. There are a number of references on the net about working with this type of tach. https://www.hazelden.ca/austinhealey/RebuildingBJ8Tach/ I'm sure that someone will add more specific information.
D
 
And depending on how proficient one is or is not with a soldering iron and a bunch of capacitors and diodes, one can always ship the tach off to MO MA Manufacturing or Nosingers for repair, probably about $150 give or take.
 
A '65 huh? I'm thinking that's before Sprites were negative ground. If your car is now negative ground and the tach is labeled pos ground (or isn't labeled)one of the problems is converting your tach to negative ground.

The other problem can be that the capacitors inside these units fail with age. If you are handy with a soldering iron, it is a simple job to replace them with modern capacitors and 99% of the time you'll have fixed the problem without requiring a degree in electrical engineering to do it (just good soldering skills).

Note:
If the tach is a positive ground unit and it has been in a car that has been converted to negative ground without altering the tach, it will have more wrong with it than the capacitors. Generally still repairable, but now, someone that is skilled is required to repair the thing. If I were faced with this situation, I would look on ebay for a good used tach from a negative ground car. The last one I bought was about $20 plus shipping.
 
The car is positive ground, but i think it was converted and dont know wheather the tach is pisitive ground or not. What i do know is that it is not working. Any methods on how to test it with out having to install it. /ubbthreads/images/graemlins/savewave.gif
 
If the tach were converted there would usually be some tape over the solder connection where the white wire was reversed. Check your battery to see which side goes to ground.
 
I believe that when tach polarity is reversed there is at least one internal diode that is reversed as well. This would not be noticeable from the outside. A google search should produce a couple of illustrated web pages on the conversion process.
 
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