Quoted from pintastic:
I think its 3-4 ohms
As a minimum, that's correct.
MM set to measure resistance (ohms), so set your meter accordingly.
Put the black on one outside lug, the red on the other.
Doesn't matter which color on which lug, mix and match all you want. Put one on the center lug if you want and measure that. Doesn't matter. There is no way to damage your coil or your machine or yourself by doing this. (power off, remember?).
You are looking for a minimum of 3 ohms. If you can't get that reading consistently across the lugs, the coil is probably dead. It might be much much higher , even 25+ depending on the type of coil and it's use. Doesn't mean one is better than the other. It's just the way that particular coil is built. Just look for a minimum of 3 ohms.
If the power is off to the machine - unplugged - you can pretty much poke your MM around anywhere under the playfield and search for readings like this on coils and diodes, etc. You can't hurt anything even if you put your probes in totally illogical places. So no fear.