hi there
first of all is the brake light/tail light bulb in the right way round?,they sometimes can go in either way especially if they are cheap replacements also check the bulb terminals are ok and not shorting out with each other .
secondly check the wiring especially the earth wire/connector plugs on the light cluster make sure they are clean and free from corrosion,small piece of emery cloth should clean them up nicely, old ford escorts have this problem creating the christmas tree light effect whenever the brake is pressed,if the earth is broken or corroded the voltage will find an alternative route causing the lights to go out or illuminate other lights instead.
hope this helps
other than looking at it myself i cant really help out more than that
good luck
