sourcing 12vdc

This is my first time here and my first time working with auto electrics.  I have a "basic" knowledge of electronics stemming from tube guitar amps.  One thing I will have to get use to is the notion that electrons flow from + to - .  That is really strange to me.  I have done some searching here to find what I am looking for.  But this is a pretty large sight and I have come up empty.

I would be happy if someone could link me to a sticky or similar that would explain the basibs of locating DC power for auto accessories.  For example, my son has asked me to help him install a CB radio in his car.  So, info/instruction on tapping into DC would be much appreciated.  If we were to take the FM/CD out of his car I could easily grab that access.  But what is the best way to get/find power for aftermarket toys in a car that is already using electronics?  I hope I amge getting my point across.  I do not want anybody to watse hours helping me.  Just need to be pointed in the right direction, to the information that is already out there.  If my spelling is bad I apologize.  I could not get Spell Check to work.

Thank You                                                                                                                                                                                                                         

i am an idiot wrote:

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Why not you let us know what kind of vehicle you are dealing with and we can let you know where you can access such a wire.  Or you can look in the Vehicle Wiring Database on this site and get your information.   

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It is a 1969 12 volt VW Bug.  I appreciate your help. I realaize it helps you to know what kind of car somebody is working on.  What I was really wondering is where do you begin (on any car) to locate power for a radio, CB, etc. 

By the way, how do you guys spell check?

Thank You

By now, we are all spelling experts.  :)

The easiest way to get 12vdc power is to go to the battery.  Fuse the wire within 12" of the battery.  This works all the time and you have virtually unlimited current (for most applications).

The second place to go would be the main ignition harness - there is usually (on most cars, at least) a high current 12vdc wire going to the ignition switch.

If you need power only when the igniton is on the main ignition wire (again usually found going to the ignition switch) is a good source.  Ideally you would use the ignition voltage to switch a relay that is fed directly from the battery as this will have minimal parasetic draw on the OEM electrical system.

Thats the "perfect world" scenario - however typically most people aren't willing to go directly to the battery because of the difficulty involved.  It also doesn't really make sense to go to the battery for a 10A CB radio.

ianarian wrote:

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Also, I got a voltage tester, one with a idiot light in the handle and a sharp pin point at the end. A wire lead comes out the handle that clips to any grounded metal. The point end easily pokes thru wire insulation and leaves no hole. It wont tell you voltage but it glows when you find a hot.

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Works fine, and safe on a 69 bug.... NOT the tool for anything built after the late 80's (I don't care how good you think you are!)

The tool is, and always will be (should be) a decent digital multi meter.

A cheap auto ranging Craftsman meter will be just as easy to use as your "idiot light".  You set it to DC volts, ground the black probe, and use the red probe to find voltages.  The key, here, is the auto ranging feature that automatically ranges the meter for you.