If your rig does not have a switch to switch the radio to house power
The very easiest is to pick up a couple of "tab" connectors (well, at least one) and an in-line fuse holder for the dash radio. With the ignition in the ACC position remove the radio fuse (or fuses) from the fuse block. Using a volt meter find out which terminals are "hot" (12 volt) and which are not. Plug wires "Tab" type ends into the "not" side of these fuse slots.
Run the wires to a house power location (you may have to run a LOT of wire to get there) and put an in-line fuse holder, put the original fuse in the holder. and that's it
You need one fuse holder per fuse
If you wish to switch between "house' and "Vehicle" power. add a SPDT switch and a 2nd (3rd) length of wire and fuse (Same as radio main) to the "Hot" slot
Hot lead to switch "Road" position
Cold lead to switch Center
House lead to switch Park side
And that's it.
A better way involves tracing and cutting and splicing wires, but that's the easy way