Rear indicator light stops flashing when braking

[Nuubec]

Ok so I recently bought a 1998 three door ford festiva and I love her! Noticed right indicator blinking at double time so changed the bulbs today, however then noticed that instead of the bulb needing replacement it must be something else - the rear indicator works fine provided the brakes aren't being pressed, soon as the brake is pressed the indicator stops flashing and the brake light starts flashing instead. Not ideal.
I can do the basics mechanically but I don't want to start messing around with the wires when I don't really know what I'm doing - I'm guessing though it's obviously a connector or perhaps a fuse issue and if I can fix it myself I will... Any ideas or suggestions would be great, thanks!

[zoom zoom]

Use a small pick to pry the contacts out, spray it with contact cleaner, and squirt some dielectric grease in.

[Nuubec]

So the contacts may be loose? I should probably be more specific, this is the first car I've owned, since I'm only just learning to drive in my 30s. My husband has had cars obviously but he doesn't know a thing about them (drives me nuts) and actually I guarantee I know more about car maintenance than he does. But that ain't much. The wires are through the panel in the back next to the rear water tank, correct? Thanks again for the help

[tooldude]

If you have the owner's manual, check that all your bulbs are the proper number. If you have any standard dual filiment bulbs, swap them with new bulbs in case of an internal short. Check any part of the wires that you can see for areas of scraped off insulation that could short to the body. It might be possible that the flasher could be defective.

[Nuubec]

Problem located to be faulty earth connection. Installed new negative battery terminals and all is well.