the switched 12 volt ignition key power right? so where would that go in the mark2?

The corresponding wire on the Mark2 is colored orange. You car's switched 12v ignition power goes to the orange wire on the Mark2. Since you already used this wire on your Mark1 installation, you should already know which of your car's wires that the Mark2's orange wire should connect to.

but what would the constant 12 volt power look like? there is got to be a defining characteristic. like a label on it or something.

The constant 12v power wire on the Mk2 is colored yellow.

The constant 12v power wire on your car is going to look different depending on which car you own. It is never ever labeled and it is not obvious.

You should have purchased an aftermarket wiring harness adapter when you installed your stereo into your Explorer. This is a very commonly-availble part. It is a plug that plugs into your Explorer's factory wiring harness and contains all the necessary connections, which should be all labeled.

If you purchased this aftermarket wiring harness adapter, its constant 12v power would likely be colored yellow and be labeled either "constant" or "memory".

If you did not purchase an aftermarket wiring harness adapter for your vehicle, and instead cut the factory harness connector off of the wires, then I cannot help you and you're on your own.