You've got to start somewhere: check you have 12V at one end of the window element, and a good chassis connection at the other.
If you don't, work logically back from there to the switch, fuse and eventualy the battery.
Somewhere along the journey the 12V will reappear; then you should know where the fault lies.
Also check that the element hasn't gone high-resistance. By my guestimations, the element should measure less than 1 ohm (ie. Not a short circuit, but close).
Even if you have to splash-out on a DVM, it'll still be MUCH cheaper to prod around yourself and employ a bit of thought rather than auto electrician.
'73 Jensen Interceptor (Resting)
Giant Full Sus Mountain Bike