ABS issue 98 dually

[98 dually]

I have a 98 12valve 3500 dually with front and rear abs the rear is drum and I believe the cause of my problem is there. When I apply the brakes not always but most of the time I get a vibration that I would guess to be the rear abs pulsating. Is there a sensor back there that may cause this. The abs light is on constantly. Please help, thanks!

 

[dudeman2009]

The rear abs sensor is located on the rear differential. The abs light could also be caused by a poor connection at one of the connectors.