I hate to ask, but as a former technical support person I have to clarify some things in order to give better answers.-
Statements like- "but if i don't get any reading out of the coil" make me ask what "reading" are you specifically looking for, as opposed to "I measured the resistance of the primary coil and it was "x"".
Which tests have you actually done and are they done correctly? I only ask because I don't know your skills but I do know most folks have a little trouble with electricity. I've actually taught the subject to aircraft mechanics and can post a whole treatise on what to do and how to do it. I just don't like to push.
Basically you need to first understand what the coil is and how it does what it does. Its called a coil but is actually two coils called a transformer. If you think about it, it 'transforms' your 6 or 12 volts into 20,000 to 50,000 volts at the plug to make the spark. It does this through a process called 'inductance'. That's another lesson though.
The two coils consist of varnished wire coiled upon itself and wrapped many many times.The two coils, the primary coil and the secondary coil, must be electrically separated from each other in order for 'mutual inductance' to occur. Also the number of windings in each of the coils determines the amount or ratio of transformation of voltage (12vdc > 20kvdc). If the two coils are touching each other, or if the varnish wears from around a coil winding (due to Spokes' overheating reason) internally the coil can no longer set up the magnetic field (part of inductance) required to work. If this occurs the coil is "shorted". You'll find no magic, nothing special but varnished wire (and in older automotive coils some oil for cooling). This is why we test the coil by measuring the resistance of the length of wire used to make up the primary coil.
The Breaker points are simply the device that breaks or collapses the magnetic field that occurs in the primary coil and when that magnetic field collapses it 'induces' (thus induction) a stepped up voltage into the secondary coil which then continues on to the spark plug.
As Spokes points outs, leaving the key on and having the points closed just turns the coils into a heater and melts the insulating waxes and can get hot enough to melt the varnish on the internal coil wires eventually causing a shorted coil.
In general if the coil primary is good (measures 2-5 ohms of resistance) then proceed with further tests. This primary coil resistance test must be done with the coil assembly electrically isolated (unplugged from the rest of the circuit) but can be done while still on the bike or on the bench.
The attached diagram is from my Clymer's and the procedures they use are are not bad (though some manuals have bad data)- good to have on hand.
Sorry if this seems too academic, just trying to help.
Larz
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