My abs/brake light comes on when I turn on the ac/heater motor blower and then the blower motor shuts down as well.
Answer: The ABS light and brake light have nothing to do with the blower motor electrical circuit. Very strange that they would effect each other. I can only think of two things that can be causing your problems on your Silverado.
There may be a low system voltage problem. The ABS computer looks at system voltage and will set a warning light if it is too low. Turning on the blower causes a quick heavy load on the truck electrical system. Look at your volt gauge or see if the battery light come on as well. If the gauge is low or the light comes on, you have a charging system problem. If not, then you may have a faulty i ignition switch. This supplies voltage to most of the vehicle systems.
The other possibility is a bad ground. Again, a quick and heavy load on a the ground side of a circuit can cause all kinds of issues.
You may want to have the ABS computer checked for trouble codes to see if there is one stored in memory for low system voltage. If so, then look into the things i described above.