12v Power Source Behind Dash

I needed to install a switch in my dash and was wondering the best place to pull power for the switch. I have a 4x4 shifter on the floor so there is a wire harness behind the dash that would run to the 4x4 switch if I had that option. I was wondering if I could use this as a safe power source and if so how i determine which wires in the harness carry the power. if not then where should i run my wires to to get a power source???

You don't say when you want the power: always on, on when ignition is on, on when engine is running.

Always on, may drain the battery so be sure that is what you want.

Then you need to buy a test light. Most chain auto parts store will have one for around $10.

Then get one of these http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F004%5F001%5F000&product%5Fid=270%2D1204

And then find a circuit of the right size and tap into the fuse box. Using the test light, you can find a fuse that has power. If you want hot all the time, turn the ignition off. If you want hot when ignition, turn the key on and find a fuse that is hot. Add the tap to supply power to you device.

//2000CAYukon