PLEASE HELP! brake light works tail light doesn't.

[burnicarus]

SO now Im having trouble with my tail light. I havent mentioned this on here but one day my tail and speedo lights stopped working and my low beam burnt out. I replaced the tail light and now when i brake it turns on but it doesnt stay on. My high beams work but the tail light doesnt work when I put it in park or when I have the low beam switch on with the bike running. What is the deal?

Is it the fuse or some grounding issue. the connection on my keyswitch looks fine but i dont know about the inside of it or the wiring. fuse maybe? im new to using a voltmeter