If you check your installation instructions, most (all?) radios want to be wired directly to the battery, especially those that transmit 50W. They can pull significant current and most circuits in a fuse box aren't wired for the required current. If you decide to wire to a spare slot in the fuse box, make sure the existing fuse box wire gauge can carry the current (e.g., is the same gauge as the power wiring on your radio). You can check the required fuse by checking what fuse is installed inline with your radio power wiring. They all come with an inline fuse. I use a KG1000G instead of a midland, so I don't have a radio to check. However, my radio uses a 40A fuse in *both* the positive and negative leg of the radio power wiring harness.
Looking at the install guide in the owners guide. It states you can either go straight to battery, or tap a fuse. If taping a fuse make sure the wire gauge (amperage is enough). The power and ground wire are both 14 AWG. I also noticed there was no yellow wire for memory.
Few other threads detail this but the short answer is 29 for constant power and 35 for power only when ignition-on. Both have fuse in them already but are spares. Tested them to be sure of the accuracy and work perfectly for my dash cam. I have a Badlands LUX so should be the same for you.
