Brake lt woes

Well part of that is to have you check the system voltage when running, at the battery, then at the tail light socket. If there is a drop in voltage of more than say .3 you have dirty connections or resistance in your switch and wires. Ground the same thing applies, there should be no resistance from your - battery cable and your ground at the tail light socket.
System voltage measured at battery,at over 3000rpm should be less than 15v.

Here is a recap of the problem .
my running light burned out and brake light kept working. i changed the bulb, thinking nothing of a burnt out bulb. now just a few rides latter, my bud stops me and say my rear running lt is out again, but the brake lt is good.
any suggestions as to where to start with this one. electrical is not my strong suit. come to think of it , i dont have a strong suite. Lol
I’m more of a jackass of all trades.



Ok i checked a few things. i have a 76kz900 with what appears to be 73 to 75 wiring, only 1 fuse.
wires to tail have good ground (0, Resistance)at wires leading to the light. i have not taken the light apart to check the bulb connections.
I only 10.2 v.at the red tail running lt wire. the bat has 12.7, and 14.7v when running.
i tested the voltage from the white fuse wire up to the ignition (key)switch and have 12.7 there. i am confused about tracing the wires back further. there are 4 wires in the block to the switch.white, red, blue, brown.the wht(power straight from bat) goes in and when i turn the key on it energizes a brown coming out.if i turn the key all the way right it energizes the red and i get 12.7 v to the tail lt.with the key in run and i turn on the running lt's , it energizes the blue at 10.5v. at no time does it energizes the red. the red at the tail gets 10.5 for the running lt. so at some point the blue at the key must join to the red for the tail lt? but i dont see that in the wiring diagram? the blue goes to the headlight switch.
at no time does the red at the switch get power?
it shows the red going directly to the tail lt.
the blue goes to the head lt switch .i dont understand the head lt switch power? the blue is on booth sides of the switch , but 1 side is actual a red that comes back to the blue.and a brown is on another terminal that leads to the kill switch.

Tried to get a verification of over or correct charge voltage.

Yes with it set to the same 20VDC scale as when checking the voltage, if it a digital, which it sounds like from your posts.
I know you've been checking and cleaning lots of connections, did you get a better voltage at the rear tail light Assy socket yet? How did the voltage drop at the junction block/ single fuse work out?
Oh and did you happen to measure the voltage at the positive side of your ignition coils?