Adding a circuit that is hot during run only

I want to figure out a way to make a circuit that is only hot when the engine is running. As it is, there is one side of the fuse panel that is hot and one side that is switched. I want one that is only hot after the engine is running. I'm building a 66 Bonneville car right now with some heavy draw items like a compressor for air suspension, a couple amps for a medium duty stereo, DRLs, and they normally would come on with the switch. How does one go about adding a run-only circuit so those items wait until the start is done and the alternator is making power?