Draw 12v from a HDD power connector instead.
I have already connected 4pin 12v plug from PSU to the motherboard, unless I connect this it won't power on. I want to connect my LCD monitor powersupply to this 4pin 12v plug from PSU. Is it possible to connect both, will the 4pin 12v plug be able to power the monitor as well as the motherboard..
Personally I don't agree with running the monitor from the PC's PSU.
Yes, it's great for a regulated 12v source. And I certainly recommend running your monitor of a regulated 12v source as opposed to directly from the battery.
However if you have any delay on the PC shutdown, so that you can leave the car a return within say 10 mins (depends on what you set it to) and have the PC still on rather than it have to boot up each and everytime you pop into the petrol station, a shop, friends house etc, the monitor will still be on and shining bright attracting the unwanted attention of thieving scum.
Then again, if you don't plan on a delayed shutdown no worries. (Oh, unless you have no shielding on the monitor, in which case it will reduce the range at which your remote keyfob will work for that minute or so the PC is on whilst it is shutting down cleanly)
If you don't want to shut down your computer when you have to turn your car off, you can install a UPS system. It will allow you to leave your computer on or in standby mode depending on system power requirements, drawing power from the auxilary battery when the voltage from the car's battery drops below 13.1 ±0.2 volts.
See the following links for the UPS controller and aluminum battery holder, (you have to buy battery that fits the holder, or make you own from 1/16 inch aluminum).
As for the monitor being on attracting theives, you can create a button that activates a black screensaver,(or better yet an animation of a very Sophisticated car alarm system) or you can buy a false radio face to cover it up.
Last edited by TheMadTinker; 10-22-2011 at 10:56 AM. Reason: additional info