12 V switched source under hood?

Personally, I would Always tie into the Engine Junction Block, But beings you asked...

There is a Red wire that comes off the Engine Relay Block. From there, it goes into a Junction Connector, splits and becomes 2 Red wires. Assuming that you have the correct wire, you may tap into that wire for your accessory.

A BETTER WAY:

Goto Radio Shack , and have them explain how you would add a breaker into a vehicle breaker pannel. Follow their directions. I'd put the new breaker near the Dome Fuse in the Engine Relay Block.

The Steaks

 

Under the hood is exposed to the elements. Read it will eventually become corroded. Given that salt is bad for electrical connections you must live in an area away from all snow, the oceans and dirt. If you are savvy enough to be under the hood with all of the high voltage just tap into the fuse box and have at it. Make your own connection point and add whatever you want to add in the way of accessories. Use underground rated wire nuts to make all of your splices weather proof to avoid the corrosion problems. Be certain that none of the stuff can vibrate into anything that can be damaged.
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Have fun voiding your warranty!

Sarcasm keeps you from telling people what you are really thinking!

 

Why not just bolt it onto the jump start post? That is a mighty convenient 12V source under the hood?

 

Hold on a second....

You want switched +12VDC and you want it WITHOUT tapping the fuse block (which is exactly the right place and right way of getting your switched +12)?

Seriously, if you're going to draw your own power from a switched source aside from the fuse panels, you're going to want to install a fusible link in-line (or similar) because if I were you I wouldn't trust anything you were thinking about installing under that hood nearly as much as I trust the stock electrical components of the car -- I would assume the stuff I sought to install was the most likely to fail catastrophically and I would either:

1) get a fuse tap and tap into a line already running below capacity
2) get a jumper and a fuse and borrow from an empty fuse position
3) if absolutely impossible to use the fuses, I'd tap into the power for the windshield squirter and install a fuse in-line to my work.

~ dan ~

Better safe than stupidly standing on the side of the road watching your car burn to the ground.