Ford Fusion Cigarette Lighter: Re-wire to Turn On and Off with Ignition?

September 4, 2013 4:44 PM

I have a 2010 Ford Fusion and a lot of electrical gadgets which plug into the cigarette lighter. The car I previously drove (for over ten years) had a cigarette lighter which turned itself on and off with the ignition. The Fusion, however, leaves the lighter socket on all the time. Because of this, I sometimes forget to unplug things from the cigarette lighter and end up with a dead battery after a day or two with the car parked. Is there some relatively-easy way for me (or a mechanic) to re-wire the cigarette lighter so that it powers itself on and off with the ignition? If so, how?

*** Pre-emptive answers to questions you might ask ***

1) Why don't you just remember to unplug your stuff?

Probably because the car I drove for the previous ten years didn't require it. I have had this car for just over three years and I still forget to unplug things from time to time, so I need another solution.

2) If you've run your battery down this many times, it's probably shot. You should buy a new one.

Yeah, I know. But I don't want to buy a new battery just to run *it* down repeatedly because of my lack of remembering to unplug stuff.

3) Your "stuff" shouldn't run your battery down in just 1-3 days; something is definitely wrong with your battery/car/etc...

I have had my battery tested by both the Ford dealer and independent auto parts stores, and they say nothing is wrong with it. Additionally, when I do remember to unplug all my accessories, I can leave the car parked for over a week and it starts just fine afterward.

4) What the heck kind of stuff do you leave plugged in that causes your battery to run down that quickly??

My Garmin GPS is enough to make it run down in 2-3 days of being parked. In addition to that, I sometimes also run a cell phone charger and a Globalstar satellite phone from the vehicle power.

*** End Section ***

I am familiar with and comfortable working with 12V electronics. I would prefer to do this work myself, but would probably refer it to a mechanic if it requires extensive removal of dashboard/etc components.

Thanks in advance for your suggestions!

posted by Juffo-Wup to Travel & Transportation (11 answers total)

Sounds like you may be looking for a shut-off timer:
http://www.groupmobile.com/docs/products/ChargeGuard.pdf
posted by perpetualstroll at 5:04 PM on September 4, 2013 [1 favorite]

Casual googling suggests that there's no "stock" way of doing this on the Fusion (e.q menu setting or seekrit OBDII handshake.) My approach would probably be to find a 12V line going to the stereo that is ignition switched (the stereo turns off when you turn the car off, right?) and use that to engage a relay that interrupts one pole of the cigarette lighter. This would be safer than rewiring the cigarette lighter to directly steal current from the stereo or another nearby ignition-switched circuit that may not have the spare capacity to charge all your gadgets without blowing a fuse or worse.

I think this would be trivially easy for a car stereo shop to accomplish.
posted by contraption at 5:05 PM on September 4, 2013 [2 favorites]

It will probably better to tap into an 12V accessory wire that loses power when your car is off than to try to modify your cigarette lighter. If not, you may have to find a fuse that is accessory hot and run it from your engine compartment.
posted by wongcorgi at 5:06 PM on September 4, 2013 [2 favorites]

What contraption said. You can pick up any SPST relay for a few bucks and wire it up yourself.

The accessory circuit will drive the switch in the relay, and the relay will drive the outlets. Make sure you get one that can handle 10-15 amps at least. Pretty much any auto-part store will have them.

Alternatively, you could wire a SPST switch in there, but finding one that can handle the max draw of the outlet (10 amps, probably, but as high as 15) will be harder than finding an equivalent relay.
posted by Pogo_Fuzzybutt at 5:55 PM on September 4, 2013 [2 favorites]

Yeah, the exact solution would be to put a relay in the cigarette lighter wire. Right now it probably runs more-or-less directly to the battery, so that it can supply a lot of current if you had an actual resistive cigarette lighter in there (which almost nobody actually does anymore).

However, the less DIY solution would be to get something like a "PriorityStart" or other "battery protector". Basically they are little bolt-on accessories that go on the battery and will shut off current if they detect the battery getting low. You typically have to pop the hood to reset them, but they keep you from running the battery down low enough that you can't start the car. They are very easy to install and result in no permanent modifications to the vehicle.
posted by Kadin2048 at 6:16 PM on September 4, 2013 [1 favorite]

There also may be a spare switched fuse bay in the fuse box. I seem to remember those existing on some cars. So you'd just find the wire that goes from the accessory/lighter socket, remove it from the lug that it is currently attached to, attach it to an empty one and insert a fuse. Or just install a new switched socket, leaving the original ones as equipped from the factory. (According to the owner's manual, there are lots of spare fuse areas, so one of them should work.)

I wouldn't mess with relays unless you had to. Just another thing to fail.

Asking another question: does your car have multiple accessory/cigarette lighter sockets? I also seem to remember that newer cars would have more than one, and different ones would run off of different sources. (Never mind, I just checked the manual and it doesn't appear that there is one.)

Another option: does your stuff have a sleep mode? I can understand the GPS unit running down the battery after a number of days, but the phones shouldn't run it down. So if you can set the GPS to shut itself off after 4 hours or something, that should work too.
posted by gjc at 8:01 PM on September 4, 2013 [1 favorite]

Pretty much what gjc is suggesting -

I found a spare location in the fuse box for something that only comes on with the ignition (heated seats or something not fitted) and used a cut down spade connector shoved into where the fuse would go (with an inline fuse (quite important)) to a replacement lighter socket. For 0v you just need to make a good connection with metalwork. It's not super slick but it's removable in seconds.

This all depends if you can get easily from the fusebox to somewhere convenient for your electronics of course.
posted by samj at 11:22 PM on September 4, 2013

Would you be willing to pay $25 for a cable that instead provides power from the OBD-II port? The OBD-II port is always on, but I know that a special cable is in the process of being developed that would only output power to your devices when the engine is on (it does that by using certain data from the OBD-II port to know the operating status of the vehicle). Something similar could be done with the cigarette lighter plug by measuring the voltage (a drop in voltage would be a proxy for "engine off") but it would likely be less accurate.
posted by Dansaman at 10:38 AM on September 5, 2013

What contraption said is what I would do. Not that hard, really.
posted by Doohickie at 11:04 AM on September 5, 2013

Response by poster: Another option: does your stuff have a sleep mode? I can understand the GPS unit running down the battery after a number of days, but the phones shouldn't run it down. So if you can set the GPS to shut itself off after 4 hours or something, that should work too.

I'm afraid neither the GPS nor the satellite phone have auto-off options.
posted by Juffo-Wup at 5:10 PM on November 6, 2013

Response by poster: Asking another question: does your car have multiple accessory/cigarette lighter sockets? I also seem to remember that newer cars would have more than one, and different ones would run off of different sources.

It does, but they are all always-on; none of the power points are ignition-switched.
posted by Juffo-Wup at 5:11 PM on November 6, 2013