Stereo & Electronics - Need help finding ignition wire

I am mounting a transtemp gauge and I need 2 find a good ignition wire to power my gauge. I am mounting the gauge in the slot below the air controls. So whats a good wire to tap into to power the gauge so it will come on with the car?

There are slots marked BATT, IGN in the fusebox on the drivers side of the dash which can be used, you just need a spade connector for it