Drawing wire from battery. How to add a switch?

[rppauto]

Folks,
I am planning to draw a wire from battery to a newly added fuse block in the inside of the car.

I want to power 3-4 devices (backup cam, monitor, radar detector, cell charger).

I don't plan to use / addon to any existing under dash fuses.

Question.
How do I do this wiring to ensure that these devices are ON only when the ignition switch is turned ON?

I could not see any good place to add a switch.

Please advise thanks

[CYANiDE]

I wouldn't use a switch, I'd use a relay. Use a fuse that currently only gets 12V when the car is on, run that to the relay.

[The Pope]

Basicilly what CYANiDE said.

Take new positive wire from battery positive to the "common" side of a relay (post #30), then from there, connect your new circuit to post #87 (leave post #87a un-used).

To control this new circuit, find a source of +12v when the car is switched on. Tap into this circuit and run a wire to post #85. Then run a wire from post #86 to ground.

That's basicilly it, but please let some others chime in as I may have missed something. Also a Google search on "Relay Circuits" will result in a lot of information as well.

[rppauto]

Thanks guys for your valuable inputs.

I now understand the concept.

I found this video.

http://youtu.be/Yu_e5u_58XE

Can you please confirm that the connections mentioned here in this video are right?

I think they don't match (85/86) with the above description (i may be wrong).

Is my understanding right?
86 = Source this power from anything that switches ON when IGN is ON
85 = Ground

30 = Positive from Battery
87 = Connect to the device that needs power


http://www.autoshop101.com/forms/hweb2.pdf [ Page 9 - 4 pin relay ]

Thanks guys.

[rppauto]

This is how i plan to do it. Any comments / suggestions?

[CYANiDE]

It's the same thing for 85/86 either one can go to power or ground.

What is the dotted line from ground to the fuse block for?

The relay portion looks correct. Not sure what setup you are using the fuse block, but looks like a backup cam and dash cam? I never wired up a backup cam but can't you tap into the power from the license plate lights or the reverse lights?

EDIT: Nevermind...Did a quick search, seems like the correct way to do it is to get power from a 12V ignition source which you're already doing, and then run the reverse light wire back to the headunit.

[rppauto]

Pls ignore the dotted line.

BTW, any suggestions on mounting the location for relay and new fuse block.

I am not sure how and where to do this.

As of now, my thoughts are to 3m tape it to left side (near under-dash fuse box) or right side.