there's one Jawa manual HERE There's some small amount of wiring info near the end.
Evidently the "black box" unit is often suspected of failure .. but the wiring itself is confusing so who realy knows what's up.. ("Search" this forum for related threads.)
First thing i'd check for is faults or corrosion in and around any switches / wires /connectors that are meant to kill the spark.. like a Kill switch or a keyed Ignition switch.
it might be wise to check all safety-related bulbs like tail and brake lamps and replace any broken ones. They are sometimes part of the ignition circuit on some bikes.
Unless one is on hand, last resort would be to track down a known good, working black box Ignition unit and swap.. i'd want to believe any Jawa CDI unit would work until proven otherwise..