I read about an incident involving a B737-200 pushback at night at Taipei. The A pumps had been selected off prior to engine start.
Engines were started during pushback. In accordance with procedures described earlier the generators had not been selected on after both engines were running. No problem so far.
As the tug turned the aircraft the tug driver was momentarily blinded by the nosewheel light which the captain had for some reason switched during the push.
Pilot says Oops - so sorry! and goes to switch off the nose wheel light switch which is conveniently situated next to the APU switch. He turned off the wrong switch and the APU died causing the A Pumps to supply hydraulic pressure to the nosewheel and the tug driver was injured when the tow bar broke.