Measure coil Villiers F12

You will need to remove the flywheel so that you can separate the coil primary from the contact breaker points or put a bit of card between the points . If it has a condenser/capacitor , disconnect that also.  You can then take a reading between the primary wire and the plug lead.
If it’s a late model F12 it may have a condenser embedded within the coil. Not sure of the resistance reading to be expected in either case.n

What is the copper coloured cable used for?

It’s just a permanent  Earth/ ground for the primary and secondary windings of the coil.

Should have said that it looks as though the cam ring on the crankshaft may be rubbing on it. If it is rubbed through the coil will go open circuit and the spark will be lost .

Thank you. 
 

I don’t think the copper cable is damaged. Its just a bad angle in the picture. However I dont really understand how the spark could disappear when the ground cable gets more connected to ground?

I got 3,2 ohms on primary side and 4,3 kohms on secondary. I don't know if that´s ok. I have also tried a spark gap test according to the picture below. I didn´t manage to get a spark regardless the gap distance. Any ideas?

To make it clearer. Rubbed right through and no longer making any connection to ground.

Aha of course. Thank you

I bought a new ignition coil just in case. Measured values on the new coil are 3.9kohm and 3ohm on the primary side.