Hello. This is my first time to post, but after reading around a bit I am looking forward to the feedback. I have a vehicle wiring project that I'd like feed back on. The vehicle is an SUV in which I have an equipment box with certain electrical needs: 1.) First it needs a heater to keep certain supplies from freezing at night (I live in the South, so nights are usually the only time that heating is needed). The truck is a diesel with a block heater. To supply heat the box has a AC heater installed with a thermo-cube thermostat to regulate and maintain a minimum temp of 35 degrees. To supply power a deditated AC line will be mounted under the hood and exit via the front grill (much like the current block heater line does) and end with a power strip. The block heater will plug into this power strip with some form of switching (yet to be determined) that will allow it to be turned as needed. Another extention cord will also plug into the power supply and run back to the box to supply AC power to the heater there. The truck will be manually plugged into AC supply on cold nights. 2.) Second there needs to be a DC power supply to the box. This will easily come from the batteries of the truck back to the box and terminate at a "power supply" strip to allow multiple applications. I'll probably run a "always hot" line and a "ignition switched hot" line. A - First application will be lights. For this, I will just find some 12vdc lights and wire them directly to the power strip with appropriate switches. B - Second application is dc supply to power a charger for a piece of cordless equipment - however, I would also like to be able to use the AC power to supply charging when the truck is plugged in on cold nights. This is the most challenging application. My thought were: For AC: the charge already has a AC power supply with appropriate current modification (110AC to 5v DC 1000mA). I can simply plug the charger into the same AC supply coming to the heater (but not be controlled by the thermo-cube). For DC: I need a good way to regulate down the 14-12volt supply from the batteries. Any easy suggestions?? There there should never be a time that the AC is plugged in while the truck is running (and therefore also supplying DC), but I figure that the dc supply probably needs to be "disconnected" while the AC supply is charging and so that when the truck is not running the charger will not be drawing current off the batteries. To do this I was going to put a relay in place between the battery and whatever converter application I came up with to drop the dc voltage. The relay power will be switched with the ignition, that way, when ever the truck is not running the relay will disconnect the dc power supply from the battery to the charger. I have attached an image/diagram of what I am proposing. Thanks for thoughts from anyone.