intermittent ABS/Brake light
 

hello everyone. I have a '99 Silverado that the ABS/Brake lights come on on the dash intermittently. I have made a few observations:

- they appear to come on when it's warmer. Bought truck last winter, they came on all summer, and now hardly come on (it's cold outside)

-When I bought the truck, I put in an electric brake controllerconnected to the proper connection on the floor (by left foot) using an adapter plug from NAPA. Light started to come on shortly after that.Unplugged the brake controller and lightsstill come on.

-they come on on a bumpy road. I turned off of a tarred road (ABS light not on) onto a gravel road and they came on.

-had wheel sensors cleaned andthey still came on.

I read on this forum that it may be 2 ground wires that have come loose and/or bad connectionsto the frame. Any idea where these areand if this may be theproblem? Thanks for any info youmay have.