Up hill racer

Looking for help with my 2005 S2000, this is my first ever post so sorry if I go on a bit. The ABS light stays on for various periods of time and when this happens the heater fan, Air Con and heated wing mirrors/rear screen will not work.

Cannot get the fault to repeat can stay on for 10 secs or 10 mins can happen from starting or when driving along. Garage want car indefinately at hourly rate to find and say its not covered by the extended warranty.

Has anybody any clues please.