Got a strange one here...

1992 Granada, 2l DOHC. It's just developed an electrical fault, randomly it seems like its starved of electric power (for lack of better words!), and nearly cuts out, sometimes cutting out completely. It will always start again right away. Am pretty sure it's an electrical fault anyway, i.e. moving the sunroof when the car's idling will make it splutter and die, even moving the windows up and down will make it struggle a bit. Ive tried the obvious, new battery and terminals etc but I dont know too much about the electrics in these things. Driving me mad, coz it runs perfectly most of the time.

Anyone got any ideas? Much appreciated.

Thanks,
Stuart