I have two convenient power ports (aka cigarette lighters) built in under the dash of my Blazer. They are always on, which makes it great for charging a phone when I'm not in the car. However, I got a dash cam and it uses a lot of juice. Twice the battery has run down and I needed a jump start. I have since removed the cam but wonder if there is a better solution - one in which I can keep the cam running only when necessary?

 

Find an ignition on only source for one of the power ports for 12 volt power, but I wouldn't just tap into a line under the dash. You may end up blowing a fuse if you do so. Better to tap into the fuse block before the fuse and add an inline fuse for the port.

Or just unplug the cam when you don't need it and plug it in when you do.

 

If you have a bunch of money to throw at it, put a Power Tamer in the circuit. It will keep the outlet energized for a preset amount of time (so the camera doesn't shut off when you get out of the car for a short time to go in a store, etc.), and it will automatically shut off if the battery voltage drops below a pre-determined level.

I've used them on lots of vehicles (including my Blazer), and they work great.

 

My solution was to add a relay tapped into the Retained Accessory Power (RAP) ciruit to control power to one of the power sockets.

You should be able to find my writeup about it in my build thread. If not, let me know.

 

This is a cheaper way of doing basically the same thing. The nice thing about the Power Tamer is that you can adjust the timer interval (up to like 6 hours) and it will still shut off if the battery voltage gets dangerously low. We use them at work on police cars and fire trucks for all the radios, lights, and other emergency equipment.

 

Power Tamer. I had no idea these existed!

 

Dang. Christine's way is too risky for me and Tom's too expensive!

 

I would give Christine's idea a shot. The wiring is pretty simple, and it takes very little power to energize a relay, so there's not much chance of doing damage to the circuit you tap into. I would probably use the switched circuit for the radio. That way, if you do pop the fuse for some reason, you aren't losing something important like the windshield wipers or fuel injection.

 

The most complicated part of my approach was tapping into the RAP circuit. I purposely made it hard on myself by tapping into it at tbe body relay block to make the installation as tidy as possible.

This could be substituted by finding a different place to tap into the RAP circuit. Off the top of my head, I can't recall where. I have the schematics for my 99 I could scan if it would help.

 

Puttster, if your truck is a 2002, it should have switched accessory power at the rear of the radio (probably dark green wire). This wire will be controlled by the RAP circuit like what Christine described. You can use this with a relay to interrupt the power on one of the sockets to make it switched instead of always on.

FYI, they changed the setup in 2003 and the factory radio is turned on by a databus signal instead, so there's no accessory wire.