1978 KZ650 is having problems starting.

I recently purchased a 1978 KZ650 this week with a known issue. The background on the issue was that the previous owner when riding home blew the main 20AMP fuse and quick rigged the connectors together to ride home. He rode it one more time like this and said he felt like there was a misfire on a cylinder and that none of the lights worked, but the oil light. I immediately replaced the battery when I purchased the bike, upon inspection of the bike with full charge I noticed none of the lights were working other than the oil light. I checked the fuse box and noticed that the 20AMP fuse was missing and replaced it. Once replaced I tried starting it, but still had no lights nor would the bike turn over. I stepped away from the bike for five minutes to grab my workshop manual with the ignition still on and the (bike right) ignition coil started melting. Does anyone have an idea why this would happen? Was the coil always bad? How come the lights wouldn't come on after replacing the fuse? Should I check the frame ground? I'm not a total novice with bikes, but with summer classes and work I don't have a whole lot of time to shove my nose in the workshop manual. All or any help is appreciated. Thank you.

The 20 amp fuse is the main and first fuse between the battery and the ignition key switch so that one blowing is rough since it could be anything causing the short and popping the fuse at this point.
Does your oil pressure light still work?
Does your horn work?
Does the brake light work?

You are going to have to break out the multi meter and start tracing wiring, I'm afraid; looking for melted wires and testing connectors for possible problems. Two wires that often fail are the Red,Red/White and the Black, Black/Yellow wires off the battery terminals which seem to erode from battery acid. - My 650 needed both of these wires replaced from battery terminals to connectors (under the seat and accessible) even while they looked good, they were both eaten-up internally AT the connectors.

It could be as simple as the ignition switch itself has failed too but more information is needed.

Do you have a good wiring diagram yet? If not, get one from the FILEBASE section here, like [ This one - 1978 kz650 B2 C2 ] in color

My oil pressure light does work.
My horn does work.
My brake light does not work, but neither does my turn signals, hi or low beam, or tail light.
The electric start switch does work also.

I have a wiring diagram that I've been looking at, but it was just the one in the workshop manual. Thank you for the color diagram a lot more clear.

Should I start with the wires at the connectors? Like the ones you've mentioned.

If you have a multi-meter handy; yes, start at the ignition switch and confirm your have continuity across the various connectors and input to outputs of the ignition switch.
You said:
- Oil pressure light works? - Yes - this is powered by BROWN wire.

- Horn work? - Yes - This is powered by BROWN wire

- Brake light work? - NO -
PROBLEM HERE IS: The brake light is also powered by the same BROWN wire as horn, oil pressure and neutral lights.
Maybe one or more connectors are corroded or melted? Both the front brake switch (hydraulic or lever) and rear brake switch both use the same BROWN wire as electrical source for the brake lights. Thus, pulling the front lever OR the rear brake pedal should light up the brake light in the tail...

Turn signal work? - NO - this has a separate electrical source - orange/green wire from ignition switch-

It's also possible, having looked at the color wiring diagram I linked above, that you have had some kind of failure in the right hand control since the BROWN wire plays a bigger role in that control including the starter button and ignition coil power as well as headlight (but by this model year, I believe all the headlight switches were bonded so headlight was not able to turn off).

In the end, if you have a meter and can trace the battery's voltage from the positive terminal through the white wire (it splits into two just before the ignition key switch but is same source wire) into the ignition switch and then use the wire diagram's ignition switch legend for the "ON" position to track power outputs for BROWN and ORG/GRN wires.
The RED and BLUE wires at the ignition switch actually get their power from the BROWN wire but the power passes through a fuse first and is simply split by the ignition switch for front and rear lighting...

You can always disconnect the YELLOW ignition coil leads temporarily if they're "melting" with the key on. One is likely to "feel" the power because at any given moment one of the two coils is connected to ground via the points while the other coil wouldn't be, so it's better to test the coils as per the FSM with your meter instead of assume any one of them is bad because it got warmed up.

The one thing that keeps coming up here as a common denominator is the key switch itself and the BROWN wire that is ultimately powered-on by the ignition switch... Just sayin'..

Good luck. Hopefully you can follow the color diagram with a meter in hand and track where the electrical source is going astray...
Be careful.
Clean every connection/connector you can, including any ground/earth terminations.
Always disconnect the battery ground FIRST and reconnect it LAST for safety's sake...

If something goes bad like the battery is not connected for any reason during running, all the lights will be burned out immediately. Don''t know if this could be the problem, but for sure don't ever attempt to run with the battery cables off.

Thanks wrenchmonkey. I finally have some free time this afternoon so I'm going to tinker with it soon. If I was to replace any of the wiring where would you suggest to go for new wiring?

You should be able to find the wire in most colors at auto parts store in electrical section. Small spools of various guages of wire & sundry terminals if needed.