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Marty Roth

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Different books show different connections.


The garage sale Dwell/Tach I bought some time ago says:

For Negative Ground Cars-

Connect RED lead to wire from Coil to distributor

Connect BLACK wire to any good ground


My older unit says 

Connect RED lead to wire from battery to Distributor

Connect Black lead to wire from Coil to distributor


These two versions give very different readings,

Which one is correct?


I'm actually using this on a 12 Volt system, but the depth of experience of our Pre-War folks is exemplary.

Thanks in advance for your thoughts



Edited by Marty Roth (see edit history)
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Assuming a 12 volt negative ground car and a 12 volt dwell meter, and it has only 2 leads, most would connect like your first example. For positive ground, you could in theory reverse the leads.


If it has more than 2 leads, or is anything weird, stick to 12 volt negative ground cars unless the instructions say otherwise.


For what it's worth, a 2 lead analog meter should be safe to try on 6 volts, too.


When the points are closed (100% "on" time), you need the meter to go to maximum dwell. When the points are open (0% "on" time), the meter needs to go to zero dwell. If it won't do that, something is wrong.


Maximum dwell is the number of distributor degrees between firings (assuming one coil and one distributor). So, thats 45 degrees for an Eight, 60 degrees for a six, and 90 degrees for a four.



Edited by Bloo (see edit history)
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