I added power ports to both of my AD's also. I decided to make them switched hot through automotive relays.
On the GMC it was somewhat easy as it was already converted to 12v. neg gnd. I decided to wire all the switched load through the relay and only use the key switch to control the relay. I run a Garmin for it's speedometer and fuel tracking option and it's power plug has 2ea built in USB ports.
The Chevy being 6v called for a different solution. I added a 6vdc to 12vdc power converter so I could run some 12v accessories but still maintain the trucks primary 6v system. I left the 6v circuitry alone but added a 12v automotive relay to isolate & switch the 12v circuitry. Currently the 12v circuit only powers a small tach and a power port.
The two power ports I picked up at a local Mom & Pop auto parts fit in both dash holes perfectly. Both are fused.
Both relay circuits are fused and I carry spare fuses and relays for just in case.
