Test tested this item with a 9 V battery. You can see the pictures. The needle moves in the test position. There is an old battery, not working inside the unit now. I didn’t have a battery that size to test it so I used a 9 V see pictures.
The Sun Tach Dwell Tester Model TDT-12 is ideal for enthusiasts who are interested in tuning their muscle or hot rod cars with accurate motor tachometer readings.
