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Jul 21st, 2025 | | | | Joined: Mar 2008 Posts: 61 Wrench Fetcher | | Wrench Fetcher Joined: Mar 2008 Posts: 61 | I purchased a Sears dwell tach meter and it has 2 leads. I can get the tach to work by hooking blk to neg and red to the coil. What is the hookup procedure for measuring "Dwell".
Thanks
Bill S
Tempe, AZ
Bill S.
Tempe, AZ
| | | | | Joined: Apr 2009 Posts: 554 'Bolter | | 'Bolter Joined: Apr 2009 Posts: 554 | Mine is at least 2 decades old now but it has a switch that you position for one or the other. Look for some kind of switch on yours.
| | | | | Joined: Jul 2007 Posts: 461 Shop Shark | | Shop Shark Joined: Jul 2007 Posts: 461 | Bill,
The positive lead of the meter goes to the coil negative terminal, or to the wire terminal on the distributor- either connection will do, but the coil connection is a better choice. The negative meter lead goes either to an engine ground or to a battery ground- not to the coil.
There probably is a 'Cal' position on the function selector knob. If so, turn the selector to that position, then before you connect the meter to the engine, connect the meter leads together and adjust the pointer to whatever set or calibration line is marked on the meter scale. That step calibrates the meter circuitry. Usually the set line is a black line at the high end of the scale, and might be marked 'Set' or 'Cal.' There usually is a second knob for the calibration adjustment. Also, there should be a black bar at the high end of the meter scale, and may be identified as 'Distributor Resistance.' When you connect the dwell meter and turn on the ignition switch, with the points closed, the meter pointer should settle in the black bar. That tells you that the primary resistance in the distributor is at an acceptable level (0.2 volts or less) for getting an accruate dwell reading.
After everything is set up, don't forget to set the function selector to the proper cylinder position if the meter has that setting- it probably has- I haven't looked at a Sears dwell meter for quite a while.
Hope this helps.
Harvester | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Dwell is measured by connecting the red lead to the coil (-) terminal, the distributor side, and connect the black lead to ground. A dwell meter is actually a voltmeter, and it's reading an average of the points-open voltage (full charging system voltage) and zero volts when the points are closed. It's expressed in "degrees of dwell" since a set of points that stay closed (dwell together) all the time would be 60 degrees of distributor rotation, and open all the time would be zero degrees of dwell. A 66% dwell reading would be 40 degrees on a 6-cylinder engine.
Jerry
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| | | | | Joined: Mar 2008 Posts: 61 Wrench Fetcher | | Wrench Fetcher Joined: Mar 2008 Posts: 61 | Thanks for all the info.
Bill S.
Tempe AZ
Bill S.
Tempe, AZ
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