1979 T140d Not Sparking

Here's a copy of a Service Bulletin from 1979 showing the wiring diagram in erm....'easy' version.



The wiring colours may be different depending on previous owner's messing with stuff (anything could have happened in the last 45 odd years) and also UK wiring colouring was different sometimes from the US colours, but essentially you want to remove any reliance on either the ignition switch or the kill switch.
Remember the kill switch basically 'grounds' out the coil so don't leave that in the circuit if you just bypass the ignition switch. It could be at fault and continually grounding.
Basically hot wire the battery direct to the coil with the two wires on the coil's positive side as shown below. The ignition is then on permanently. Obviously take this wire off when you have finished your test.



If there's still no spark then it's one of the remaining electrical/electronic parts - coil/s, the amplifier, or the pick up under the points cover. The wiring to/from these components would be the greatest suspects - check the continuity on all of them and whether they are grounding.
If you get a spark with the above then you need to isolate either the kill switch or the ignition to identify the fault.

There should be some better electricians along shortly as this forum has some people a whole lot better at electrickery than me.

Let us know how you get on. Best of luck.