79 kz400h tail light not working

Brake light works fine. I can lift the seat and apply power to the to the tail light connector and the tail light will light.
I have a 74 - 77 service manual, but wiring may be different on a 79.
Can someone share a 79 wiring diagram? Thanks

It´s the same wiring, red wire (tail light) get power by the ignition switch in park position (white wire battery) and blue wire in ignition on position (switch internal connected).

The problem turned out to be within the ignition switch. To fix, I jumpered the the brown wire (which is hot when ignition is on) to the red tail light wire. I never use the "park" position any way.

Did you investigate the soldered connections inside the ignition switch? You might be able to fix the problem.