Im working on a 1992 Seagrave fire engine with an 8v92. I was asked to pull the alternator because of a low voltage problem(10.5-10.8 ) and have it checked. So i started the engine before i removed it to verify the problem and i noticed the alternator was not spinning nor was the middle accessory drive pulley behind the blower. There are 2 accessory drive pulleys of the back of the motor, the one for the A/C compressor on the drivers side works fine but the one directly behind the blower spins free but is not being turned by the engine. Any input on what will cause this could be appriciated but i dont want to get in over my head.