when left indicator light is on brake lights flash?

possibly earth / connection fault. do as clive says to the plastic plug on the end of the wires. you will need to disconnect the plug and blow it out / clean it/ try to scratch any rust or deposits of of the metal contact with a screwdriver. this will help to ensure a better contact.
in addition, where all of the bulbs screw into will probably be a plastoc board with metal strip connectors. if you see any greenish rusty deposits on it, clean them off. also give the board a spray with a penetrator like wd40 or some cleaning solvent.

hope all goes to plan

markkoz
December 2007

Hi Andy, common fault on many modern cars. You will find it's just a poor connection. Find the plug connector located on or near the light cluster, unplug it and douse it penetrating oil, work the connector on and off a few times to work the oil in. This usually does the trick.

Clive
December 2007