Braking question

Hey guys,
I have a 92 ranger with ABS. Lately I've noticed that during normal braking, The truck seems to pulsate, not the pedal which would indicate warped calipers, but the whole truck itself.
Also not too long ago the Rear ABS light came on during startup, but a few minutes later would go out and would reappear from time to time. Lately it hasn't been going on so I didn't think anything of it.
Could a faulty RAB sensor be causing this or is it something else?
Thanks

if the abs light comes on at all, something is bad.your truck only has rear abs so it could be one of the sensors are bad. also check shoes and drum conditions.drums could be warped or worn.

Thanks for the reply. The rear brakes are due for a change anyhow.