Bizarre Battery Problem

[nailer]

Hi there,
First time posting from a newish elise owner (bought my Mk1 111s November 2003). I couldn't get to work this morning as the battery was completely dead - took the wife's Ford Ka instead. Chatting to my neighbour this evening he tells me that the last couple of nights he has noticed my brake lights coming on and going off about 15mins later, this happening about every half an hour. Presumably this accounts for the flat battery, but has anyone got any idea what may be happening before I take it to a Lotus dealer for a radical cash withdrawal? Incidentally the only modification I have made has been the addition of new speakers, a small amp and new head unit by a reputable car audio dealer in Leicester.
Thanks
Andy

[tupolev]

try this
www.elise-faq.info/content/brakes/index.php

tup

[nailer]

How random is that??? Thanks, I will try that tomorrow.