How to find electrical fault on Ford Focus Ghia 1999?

My Ford Focus Ghia 2.0 petrol has recently developed an electrical fault. Previously it would occasionally refuse to start and I eventually bought a new battery. this seemd to cure the fault but now the car suffers in wet weather.
when driving in rain the ABS and traction control warning lights come on, followed by battery warning and door alarms. car will then lose power and come to a halt. waiting for a few minutes the car may then start and drive but without much power. I think there is a short somewhere. Battery earth is fine
any experience of this?

Pete T
July 2008