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I have a Snap-On Dwell-Tach and I connect its yellow wire to ground (6v positive) and its black wire to the distributor side of the coil. Works fine. Now as to yours, you do not need a battery to use the dwell or tach functions - connect yours to the distributor side (green) of the coil and ground (Black) and that should give you dwell and tach readings. The remaining wire from your instrument (red) is for determining system voltage - generator or alternator. I assume you are working with a 6v positive ground system. In summary, connect the green wire to ground and the black wire to the distributor side of coil and this should give you dwell tach. The dwell tach function measures across the points (positive ground and points (coil side. I had to reverse the wires on my Snap-On - yellow to ground and black to distributor side of coil. Should work - give it a try. You are not putting battery voltage to tester at this point. If that works, connect the red wire to the neg of the the 6v battery. Yes, the red wire is always positive, but see what happens when the green wire is connected to ground - positive-to have the dwell tach operate. Remember, we are dealing with a positive ground system (6v) and the red terminal is only for measuring voltage and your meter will read 6v - do not need a 12 volt battery. Confusing? Positive ground requires the reversal of the green and black wires.