instrument cluster...HELP...

Help can anyone shed any light on my problem, after leaving my p reg p38 parked up for three months, i wasnt suprised to have to jump start it, but now all of the warning lights and high beam lights and indicator lights are perminantly illuminated...even with the ignition key removed... i have tried a new instrument cluster with no difference snd it looks like a short circuit...any advice very greatfully received...

I'd start at the BECM, make sure all the connections are good and there's no water in there.