Hard-wiring cameras into the car is something I looked into in recent years. I contacted Direct Line, my (then) insurers who told me that even if they were fitted by a professional auto electrician, they would load my premium as I had modified the vehicle. My current insurers, Admiral, told me the same.
The end result is that I have forward and rear facing cameras powered by the 12v socket, but not hard-wired. Cameras can be a double edged sword as they can provide good evidence of wrongdoing by other road users, but should you be the wrongdoer in any way, could serve to provide evidence against you.
If you have cameras hard-wired in and declare the modification to your insurers, they are likely to want footage of an incident you report to them. You can hardly deny having the cameras fitted! If you have the cameras hard-wired and don't declare the modification to your insurer, a future claim could be affected because you haven't declared the electrical modification. With my set up, in the unlikely event that I do something wrong, I can whip out both cameras very quickly, clean the suction marks off the windows and the cameras were never there.
Having said that, my preference would be to have permanent cameras in my car, but until an insurer gives me the nod that they won't load a premium against me for having them fitted, I'll continue with my ad-hoc set up. Some people may say that it's such a trivial thing that insurers would ignore such a permanent installation. I'd rather not take the chance on that.
