I've had my TY 175 for a few years now, but the other day I decided to put the lights on it. everything works fine apart from the brake light, that's powered from the yellow wire, it's came off the coil and I can't figure out where or how it goes back on from the wiring diagram in the manual any help would be great, Thanks

Are you saying the yellow wire from the coil is broken off? if this is the case then you will need to take a close look at the windings to find the end where it broke off from, you should be able to pull a bit out and then remove the lacquer from the copper and then solder the wire back on. looking at the wiring diagram it looks like the horn shouldn't work either as this is fed by the same wire. hope this helps.