Thanks James, and that is what I am fishing for. The sensor on top of the reservoir is nothing but a 2-wire plug-in on the outside, and no moving parts accessible. From what I can tell, there is no pressure diff bank like on 89 and below models. So somthing in the presuure in the reservoir may tell the switch it is out of balance and set the light. All I can do is rebleed the system and see if it responds, I guess--what a pain.