Help Please!

for some reason if i have loads of electrics on the rev needle jumps about and the lights dim, so if i have lights on and fans, the rev needle sits about 2k higher than its revving, then if i press the elecy windows i can get the needle to spin right around?!

anyone have any ideas?

took this video of just clicking the ew switch...

http://www.youtube.com/watch?v=KCai1kIwBmE

I went to put my windows down today and the rev needle is now stuck below the nib it sits on when off!

1994 BT Escos by the way..