Ray Singh
Posted a lot
More German exotica in my garage now
Posts: 1,984
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May 26, 2020 21:40:33 GMT
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Hi all - thanks for reading. I have been given a few Porsche 944 coolant and fuel gagues by my freind to repair. These do not work in the car. I only have the gagues here in my possession - so how can i test these pleae? Do i apply a voltage across the terminals? Its like this:  Any help appreciated. |
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If they don’t have a dedicated driver applying 12v carefully across the terminals should have the needle climbing to ‘max’
If they do have a driver you’ll need someone more intelligent than me!
Take care not to hold it on for too long, and Chechen which way round give got the polarity
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melle
South West
It'll come out in the wash.
Posts: 1,983
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May 27, 2020 18:44:09 GMT
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Make sure they're 12v first, many gauges operate in a 0-5 or even lower voltage range. I wouldn't think polarity matters.
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www.saabv4.com'70 Saab 96 V4 "The Devil's Own V4" '77 Saab 95 V4 van conversion project '88 Saab 900i 8V
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May 27, 2020 19:46:33 GMT
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Looking at this wiring diagram, it suggests that you need +12V DC to power the gauge and a variable voltage of between +12V DC and 0V DC to drive the position of the needle. A picture of the back/connections would also help. |
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You should have three terminals: Plus, minus and sender (or only plus and sender if the housing is made of metal). Get a not too small potentiometer, 500 ohms or 1k are fine.
First connect 12v* to plus, minus to minus and 12v to sender, the needle should move to max.
Then connect 12v to plus, minus to minus and the potentiometer between "sender" and minus (the center connector and one of the outer connectors on the potentiometer). You should be able to move the needle by turning the potentiometer.
Be patient. Some instruments are damped, it takes time until the needle moves.
*) Some instruments require a stabiliser for 10V or so, but for a quick check this is not important.
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