The radio harness has a wire that is powered up when the ignition is turned on, a wire that is always live and a ground wire. I spliced into each wire, I have a Scosche plug adapter for my radio so it was easy.
I used an insulated female plug on each wire and fitted male plugs to the dash cam wires. I wired up a Garmin 45 dash cam with the parking accessory which has the transformer in the wires. Hard wiring a unit that uses the plug in the cigarette lighter socket would be a pain and that is why I purchased the dash cam parking accessory.
These units and the GPS units generally run on 5 volts so a transformer should be easy to find. Check the voltage of your unit though. Is it possible to run a GPS unit and a dash cam from one transformer?
I have had no problem blowing fuses due to the load of the dash cam. I had no problems with the same setup on my previous dash cam which was also hard wired, unfortunately the cable was not compatible with the new dash cam.
I would urge everyone to get a dash cam, a friend has decided to fight a ticket in court which he feels is unjust, a dash cam would have shown the true events which disagree with what the cop saw. A dash cam could have saved him $400 if he had one. If you cause an accident you had better hide the camera though.
I may fit a rear facing camera some time as extra insurance, I do have a cheap spare to use. I find the dash cams that use the sticky pad to attach the camera to the windshield to be the best, the suction cup ones tend to fall off. The sticky pad can be removed with dental floss just like the trunk letters.