Advise? Heater won't work!!

[Paul Romero]

I recently got a '71 lwb and I can't get the heater to work, all the cables are attached to the panel, I tried to remove the box inside the engine comparment but is glued shut some wires in the firewall on the driver's side are cut, is it possible that I'm not getting any power to heater, how do I find out?? any advise will be appreciated. Thanks in advance