Easy, you take it out and give it to me!!! i don't think there is a switch, it's either blown or a wire isn't quite right. Probe to see if there is power going to it at all when the radio is on, it powers with the radio if I'm correct. I have an aftermarket one in mine so I don't know to much about the OEM ones.
No switch. With the earlier model Tracs there was a grounding issue. In my case, it was a pinched (cut) wire under the passengers rear seat.
Also, make sure your base is turned way up and the balance of the speakers is set correct just to ensure that you are actually asking the system to work...