OK, so my rear light doesn’t come on but the brake light part does, what could be the problem, bad earth? It’s an LED light, so unlikely to be filaments.
Sounds knackered fella
Are the lights on a different fuse to the brake light? dipped and main beam headlights working? If they are LEDS I’m assuming they aren’t stock, so unless you fitted them yourself I’d be following the trail of dodgy Halfords connectors that the DIY’er inevitably uses. A multimeter should narrow it down fairly quickly 
it could be just the brake light switch…if so only a few £ to replace…
Could be, if his brake light wasn’t coming on…
muppet moment by moi! 
my led bulb did the same probably lose wire that needs soldering back on , is it a led replacement bulb or a led tail light unit?
Bike’s knackered. Sell it cheap and buy a Honda 
check sidelight fuse
check see if bike has parking light setting on key to see if front one works also as it will be hard to see on normal light setting