Brushes are shorted to ground.

The brushes go to rotor. The rotor has a spool type winding connected to slip rings. The brushes ride on slip rings. By removing the brush carriers, it should be possible to reach meter probes to the slip rings and check continuity to pulley. The rotor winding is only a few Ohms, so what you measure on each should be similar. The winding should isolated. If the winding is isolated, then the short is a problem in brush carrier insulaton, missing insulator washer..... or other problem. If the rotor winding has short to shaft, it is not easily fixed, but could be changed out.