I'm in digest mode, so pardon me if I'm explaining something that has already been "splained."
The Primary circuit is very simple - the primary coil winding is grounded on one end and the other is connected to the points, which are grounded, and to the "P" lead terminal. The magnet spins by and with the points closed current builds up in the primary coil. Then the points open, stopping the current flow. This causes an inductive surge (high voltage - about 100+ volts), which is then transformed by the secondary winding to spark plug voltage. All the ignition switch does is permanently ground the primary coil in parallel with the points, preventing the voltage surge. The resistance of the primary coil is very low, less than 1 ohm. If you read the resistance to ground you will get
a zero reading if the points happen to be closed and a very low reading, usually mistaken as zero, when the points are open. Sorry for the long explanation, but what you are reading is probably normal.
I use a simple ohmmeter to set timing, but noting the very slight difference when the points open. But the prop has to be turned very slowly or the voltage surge will make the meter go kablooey.
Gary Casey
I tried to start my IO360
today and discovered that the P-lead on the Slick magneto seemed to be shorted to ground. When I diagnosed with a vom, I found that the p-lead stud on the mag IS a ground. My question: what is the point of grounding the P-lead if it is ground already? This is a new mag run only one hour at Superior on test stand. Someone please explain.
Ed Gray Dallas