ABS and brake light on at same time

A few months ago my ABS and brake light started coming on while driving. They don't light on start-up, but after I start driving - maybe 5 minutes, maybe 30. When I turn the truck off and restart, the lights are gone - at least until I drive for a while.

About a month ago, something else freakish happened. My gas gauge started dropping to E if I sat at idle for a minute or two. While driving the gauge acts normally, but at stop lights the gauge will drop if I stop long enough.

I have heard that on some vehicles the circuit controlling the brake system is tied in to other systems and makes funny things happen - like losing the odometer numbers on the digital odometer. I'm wondering is this is what's happening here.

Will a bad sensor or an improperly adjusted speed sensor make both lights come on at the same time? Is the speed sensor on a 2000 in the rotor area, or is it at the differential, as in some vehicles? Has anyone heard of multiple problems being caused by the brake diagnostic system? Thanks for any help.

either an elctrical problem somewhere or and this is what happened to my company truck twice -- the abs light would come on as well a various others at random - turned out to be the sighn of a failing pcm - 1st time truck just went dead after about 2 months of this happening 2nd time i didn't let that happen . dealer can check the pcm .