Major sparks when reconnecting batteries

I have a Volvo 1999 VNL.My batteries died because I left an interior light on for several days. After successfully charging ( I had disconnected the positive cables but not the negative ones ) I tried to reconnect the cables to the baterry bank which resulted in major sparking. I removed the negative cables, reconnected the positive cables and tried to reconnect the negative ones which resulted in major sparks and a whirring sound from the engine.
Can anyone diagnose my problem?
Thanks for your help.

 

Thanks for the quick replies.
It is definitely wired correctly since the cables are so stiff, color coded and of a limiting length it would be nearly impossible to screw up the cable connections.
It does sound like the solenoid is stuck open or a relay is open(?). Every time I touch the negative, heavy cabled ground to the battery there's definitely the sound of a motor turning over.