Hmmm, tail light doesn't work at all. Brake light etc

Having an issue with my 78 KZ650. The old headlight melted on me and I pulled it off and didn't mark the wires. The old headlight had built-in directionals as well.  The new headlight does not have directionals and I don't have directions on the rear brake light as well (I live in Florida).  So when I got my new headlight I, I found the wires to turn it on with the ignition and it seems to go from high beam to low beam, but now my rear brake light does not work at all.  Nothing happens when I compress the front brake whoever or the rear brake pedal. The brake light does not even come on. Could anybody help me to do some problem? Exactly what wires I should be looking for for the three wire headlight to make sure it's correct and make sure they rear tail light gets power please? There's a lot of information on here but I just can't seem to find the right stuff fix the issue. I'm ready to start writing again as I'm completing the build. Thank you all in advance

I think you have to try to switch the wires. LED lights are like diodes and need the correct voltage and polarity.

Black/Yellow = ground or negativ
Red  = 12 Volts+ ignition switch on
Blue = 12 Volts+ break light switch

 
 

As shown in the diagram, the headlight has a small plug for the bulb and three wires.  They are Red/black, Red/yellow and Black/yellow.  They have male connectors and should connect to the same colours in the main harness.  From the harness side The black/yellow should have a double female connector.  From memory, one of the others does as well but I can't remember which one.

Did you modify the wire harness?
In previous posts you mentioned how you wanted a minimal wiring harness for your bike.