HELP! I think it's electrical

73 Z1. Doing a cafe build so it has not been started in a year. No engine work done since it ran last year, just new forks, swingarm, shocks etc. Started right up yesterday and settled into an idle. Rode it for several blocks and it began to backfire on acceleration. Very sharp, almost like gunshot backfires. Had to stay in first to nurse it home. Any attempt to accelerate and it stuttered and backfired. Pulled into the garage and all electricals were dead. No starting, no instrument lights, no headlight, nothing! Had the battery checked this morning, good voltage and 235 amps when loaded. Reinstalled battery this morning, all lights are on and bright , starter turns over easily.
Any idea's on where to start looking?
Thanks in advance. Lewisj

Check your charging system.

Assuming it won't run, I think you need to check voltage to the coils.

You should have near battery voltage at the positive side of the coils.

The negative side of the coils go to the points. If the engine is stopped so the points are closed, the negative side of the coils should read near 0 volts. If the points are open, the negative side of the coils should read near battery voltage.

(The black wire of the meter should be on the battery negative terminal).

The most likely place to have voltage-loss issues is the kill switch. After that would be the ignition switch. After that, the wiring between those switches and the one going to the coils.

Based on a 75/76 Kz900 diagram... the power wire coming out fo the ignition switch is brown. It goes to the kill switch area. Then from there, the power wire for the ignition is red/yellow to the coils.

I agree with you loudhvx. The more I thought about this the more it sounded like the kill switch. The switchgear is new, but I checked anyway and made sure there were no bare wires or grounding. I cleaned up all the electrical connections under the right side cover, in the headlight shell and tightened the positive and main ground wires off the battery. It started right up and ran well for a short ride before the rain hit. Hopefully, I will get out tomorrow for an extended ride and take it up to freeway speeds . Thanks for your help! I will let you guys know how things went.