Measure resistance¹.
The grade of insulation is that much better, the higher the
insulation resistance.
If insulation is perfect the instrument needle will defect
completely in range x 1 K O show an infinite reading.
Replace distributor cap if cracked or burnt.


¹ See specifications

Pull out ignition cable; remove distributor cap.
Note when fitting: Be careful that ignition cables are
installed correctly (firing order 1 - 5 - 3 - 6 - 2 - 4).
Coution! The outside series of numbers applies ton transistor
ignition systems.

For cars with stereo suppression:
Disconnect ground cable and wire 1.
Remove distributor cap and remove suppressor from
distributor cap by pulling down.