Well, this one has me flummoxed. Basically, when the lights are turned off, the brake light functions as normal for both the front and rear brake switches, but when the lights are on (And I always ride with dipped beams on for safety reasons), the entire rear light turns off when you pull the brake lever/push the pedal. Sometimes it just turns off entirely, sometimes it goes off, then comes back on right after with the brake light on and sometimes nothing happens. As i'm not too good with electrical issues, this has rendered me slightly clueless. Anyone have any ideas where to start looking?

Cheers!

First thing I would do is strip the rear light down and give all the contacts a good clean, then check that you have power at the two terminals in the back light, sounds like a dodgey contact in there somwhere.

sounds like some water has got into the bulb holder to me causing a small short between the brake light and tail light contacts (as a rule rear light bulbs tend to have two sets of contacts on them, one for tail light one for stop light)
Do what biker 838 said take off the back lens, remove the bulb and give evrything a good look over and clean, pay particular attention to the bulb holdermake sure everything in there is nice n clean and that should sort it.

Righty ho then, i'll tear the back light down this afternoon and give everything a good look-over. Thanks!

Well, a bit of an update. I had everything apart and cleaned it all up, there was a bit of rust and such but nothing major. Gave it a blast of WD40 to drive any water out and re-assembled it. There's been absolutely no change at all. it's still dodgey as is described in the first post.

Bad earth somewhere, that would be my guess.

Have you got a simple circuit tester to check whethere there's power to the light fitting? Something like this that lights up if there's power...
Click to view attachment

It could be a connection further back, follow the wires back and clean up any connections also check for bare wires.

I agree. Definitely an earthing problem. Try cleaning (by cleaning I mean using a wire brush or emery cloth) all the contacts of ALL the connections, especially the earth wires to the frame. Rub them till they shine. By clean, I mean electrically clean. A film of oxide corrosion or rust will stop the flow of electrickery! Don't forget to emery or wire brush the bulb connectors.

I'll get the circuit tester out and start following the connections back and cleaning them up as I go along. Cheers!

Well I think I found the problem. I checked around with the circuit tester and it led me back to where the rear light it connected to the back of the bike. In what seems to be a tremendous design flaw, the contacts are exposed and on the inside of the rear mudguard, right at the top, meaning that they receive all the mud, spray and salt that you get off the road. After scraping away about 3 tonnes of mud and muck I finally found the contacts...Rusted to buggery. Gave them a clean with a wire brush and some wire wool, got all the rust off and re-assembled it all again. Everything worked so I coated the contacts in liberal amounts of WD40 and Vaseline and fabricated a small plastic cover to protect them from getting messed up again. All in all i'm rather pleased with the job.

Excellent!

well done mate bad earth would have been my next suggestion