PIR lights are incredibly useful. But rather than have the problem of wiring them in to the 12v circuit, I've fitted a number of battery-powered PIR lights, in the fridge, in a cockpit locker, and in the cupboard under the heads sink where all the seacocks, etc, live. I got them from Banggood (
http://www.banggood.com/buy/SKU184604.html) and they cost about 4 quid each. As soon as they detect movement, they light up. And they are light sensitive too, so they only work at night.