The ignition wiring on these is fairly simple, thus testing is fairly straight forward. 

Assumptions

• We assume this bike was known to be in running condition at sometime during your ownership in the recent past.
• We assume you have the stock 1979 Airhead ignition, which is points & condenser inside the 'Bean Can'.
• We assume that each connector disconnected during testing will be coated with an anti-oxidation paste before being re-connected. 

Procedure

• Unplug the Green/Blue wire from the ignition coil pair. Insert a mechanic's test lamp into the wire's connector. With the clip end connected to the cyl head fin, the tester should light up when the ign key is turned ON. Fiddling with the handlebar Kill Switch should make the light go ON/OFF appropriately.
• Reconnect the Green/Blue wire.
• Inspect for the presence and then the condition of the short Black wire connecting the 2 ignition coils together. 
• Remove the front engine cover. Closely inspect that the ignition wire to the Bean Can was not crushed when the cover was last installed. 
• Remove both sparkplugs. Plug them back into their Plug Caps. Lay the plugs on the unpainted cyl head in such a position that the hex portion touches the cyl head, but you can see the spark gap.
• Open the Bean Can. Using a small screwdriver, manually make an electrical connection across the ignition points gap. With the Ign Switch ON, you should see/hear both spark plugs fire. 
• Fully service the auto advance unit, including NEW auto advance springs. Replace the points and ignition condenser. Strobe time the ignition at high RPM (~3000) using the 'F' (full advance) mark. 
• It is also HIGHLY suggested that you also replace BOTH spark plug wires and BOTH spark plug caps if you do not know when this was last done. The wire MUST be 7mm metal core. The caps MUST be 5K Ohm; most people use NGK brand caps. Or, you can get the wire/cap assembly from Motorrad Elicktrik.

Hope this helps.