I'm a pretty good wrench but wiring is where I fall short. When installing various, aftermarket electronic gadgets they normally say "find a switched power source." The fuse/distribution block is always hot. Obviously I don't want devices running when the car is off. What's the best way to tap switched sources and where?

 

What are you trying to hardwire? If using map light harness, just try every single wire while turning your key to accessory and see which one turns it on. Same with fuse box. Just make sure you have a good ground.

 

Next will be an air fuel ratio gauge that they said can be super touchy to voltage fluctuations and flawless grounds that are close to each other are prefered. Thanks for the info. By the way. How did you get that huge photo to post in your reply?