I just got an electric exhaust cutout and I was planing on wiring it up myself. The manual says I need to connect it to a switched 12 volt sorce or to a swich fuse in the fuse panel. What are some under-dash switched 12 volt sources?

anything that comes on with the key in acc position. Anything you manually turn on and off like radio, fans, windows. You can always add your own switch, they are like a dollar or less for a toggle at autozone.

In the fuse panel in the door/dash there is a few switched sources in there. Use a test light. I believe the one in the bottom right corner is a switched source. If you need further clarification let me know. I used one of those sources for my Driving lights.
Cheers
Evan

The best place I've found for running accessories is the little fuse box that is under the dash, next to your left foot on the floor. There are several constant 12v sources, as well as some switched as well.