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Discussion Starter #1 (Edited)
Are there any common failure modes for the dash mounted tachometer (GT or aftermarket)? I have the 12V feed, a ground with 0 ohm continuity, and the car runs with the tach feed wires bridging the coil (-) and points. Just no needle movement. Always good answers from this forum ... thanks, Hans.
 

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Is this the tach provided by Smiths? The Smiths tach is typically a current sensing tach and has two wires that go to the coil / distributor. The wires are connected in series with the points. One wire would typically be connected to the coil negative terminal and the other would be connected to the points. If it is this style of tach, it will not work with the wires connected between the coil + terminal and the points if the points are still connected to the coil negative terminal. This would effectively put a short directly across the coil and the car should not start. If the car does start, it indicates that there is an open circuit in the tach sensing circuit. With this connection, you would have applied 12v directly across the low resistance sensing circuit in the tach which would have resulted in a lot of current and something probably melted and opening the circuit.

Again, these comments only apply to the Smiths current sensing style of tach.
 

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Discussion Starter #4
Thank you for the detailed response. I mispoke in the OP and meant to say coil (-) terminal; now corrected. It's a factory Volvo Smiths unit. Took it apart and found a separated wire at a solder joint; will reattach and test. At least I have the opportunity to replace the green tint light film that melted over the years.
 
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