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In my 2006 ford ka the cigarette lighter socket is always on, which means that when I turn off the engine I have to unplug the USB thingy I've got in there. It's a bit annoying and I'm constantly worried that I've forgotten to unplug it and I'll come back to a drained battery. I know that the battery probably won't drain completely overnight but it's still annoying. How would I go about making it so that this port only turns on when the car is on? I have things constantly wired into it so I need it every time I drive but only when I drive. Is it something to do with a fuse???

Thanks in advance.

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    Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Dec 20, 2018 at 17:14
  • You comfortable with some soldering? a simple relay feeding the port power that is triggered by a wire that only has power when the key is in the on position will do the trick.
    – DatsunZ1
    Commented Dec 20, 2018 at 17:35
  • yeah, think I'll wire it into the radio
    – Issy Szemeti
    Commented Dec 20, 2018 at 20:33
  • Don't need to solder. You will find there is a connector that goes from the cigarette lighter to the wiring harness. Typically it's a simple 1/4" or 3/6" spade connector. Put a male and female of those on the relay contacts (if it isn't already).
    – Harper - Reinstate Monica
    Commented Dec 21, 2018 at 1:24
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    An always-on power port is quite useful for certain applications.
    – Criggie
    Commented Dec 21, 2018 at 3:21

6 Answers 6

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This behavior is by design and it was the same on pretty much any Ford of that era (at least it was on the Mondeo, Fiesta, Fusion and Focus IME)

You can modify it to come on with the ignition but not without a little bit of re-wiring so it depends on how comfy you are with some basic electrical work.

Essentially you need to wire a relay into the the 12V wire for the cigarette lighter and use something that is only live with ignition on as the trigger wire for the relay (the "ACC" wire running to the radio is a good candidate).

While not particularly complicated electrics I'm not sure I'd recommend it as a DIY job to someone unfamiliar with electrical work in general - the upside is that any auto electrician should be able to do something like this for you in less than an hour.

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  • Every car that any of my friends have ever owned which received unskilled electrical work has ALWAYS had electrical problems for the rest of its existence. I wouldn't even trust a mechanic to be honest. I own a 2011 Honda Accord and inquired with a Honda certified mechanic shop about which automatic transmission fluid do I need for my car and the guy told me that I cannot perform an ATF change myself because there is no drain plug nor dipstick for it. I said thank you and walked away promptly before he could get the chance to lower my IQ any further.
    – MonkeyZeus
    Commented Dec 20, 2018 at 18:46
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    @IssySzemeti, instead of modifying the existing one, ask a mechanic or an auto mod store to wire up an additional cig plug that turns on and off with the engine; If you later have a need for one that's always on, you'll feel like a genius.
    – schizoid04
    Commented Dec 20, 2018 at 22:21
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    @MonkeyZeus he may not be lowering your IQ. That is true for some cars.
    – Harper - Reinstate Monica
    Commented Dec 21, 2018 at 1:19
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    @MonkeyZeus Car mechanics are known to be dishonest, at least here in Germany. Hidden test repairs often come out with unnecessary items billed (plus the fact that they miss a few real problems).
    – Peter - Reinstate Monica
    Commented Dec 21, 2018 at 7:13
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    @Harper I am aware that other cars have a sealed transmission but other cars don't concern me when I am asking about my car. Given that I located the dipstick and drain plug before ever visiting the shop I would have hoped that a Honda dealership mechanic would be informed enough not to mindlessly say such things.
    – MonkeyZeus
    Commented Dec 21, 2018 at 14:09
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I believe this would need custom wiring to be switched on and off with the ignition. Your factory lighter socket is not wired to do this.

I do not like making modifications that change the factory wiring or can not be easily reversed, so this is my suggestion. Get a fuse tap. This will allow you to create a new circuit off an existing fuse. Use a switched, non essential circuit, like switched power for the radio. Run the fuse tap to a new 12v lighter socket. The power wire runs to the center back or the lighter socket. You will need to run a ground to the case of the lighter socket.

Example of a fuse tap

New lighter socket

I'd look for a lighter socket like this with a bracket. You can use double sided tape (think command strips) to mount it so you are not making a permanent change.

Alternately, you could run power from the new circuit to the existing lighter outlet. This may be more difficult to run the power wire through the dash. If you do this, remove the fuse for the current lighter circuit, so you do not have a live wire hanging behind your dash.

EDIT: Based on Paulster2's suggestion. You could use a 12v to USB (socket, or mini) if your only intention is to use this with USB devices. My only concern with this is if it is designed to work with the fast charge feature on your phone. Some of these are available in a kit with the fuse tap.

Here is an example of one.

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  • Along this line, but what I'd consider even better yet, is to wire in a power source off the switched line to charge the phone. A phone charger would be very easy to wire in and you wouldn't have to worry about overloading a circuit if you (or someone unknowingly) plugged in something to the 12v power adapter which couldn't take the amperage.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Dec 20, 2018 at 17:58
  • Thank you for the suggestion. I added a section with a 12V to USB adapter.
    – rpmerf
    Commented Dec 20, 2018 at 18:23
  • Hard-wiring a USB port rather than a standard cigarette lighter socket is a bad idea because nobody with a clue wants to plug their phone into an unknown USB port to charge it. A clearly power-only socket lets anyone who's riding provide their own known-safe 12V-to-USB charger rather than needing to have a USB condom.
    – R.. GitHub STOP HELPING ICE
    Commented Dec 21, 2018 at 16:06
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Unless you are leaving something actually plugged in and charging all the time, the charger itself is probably only running a little LED which is negligable in the context of the parasitic load from other things in the car. (clock, alarm, etc)

Even if you were to plug in a cell phone with a fully discharged battery, for example, which has maybe a few Ah capacity, the battery in your car is about 50 Ah, so in the worst case you might drain ~5% of your battery capacity in charging the phone.

If it's just the LED, they draw more like 20 mA IIRC, so it would take ~1000 hours for one to drain 40% of your battery capacity. If you are leaving the car this long I would just unplug the device!

Personal experience is that I have a phone charger with a little blue LED that is plugged in all the time in my car, and sometimes don't go anywhere for weeks at a time. I don't notice any trouble starting it after this, even in the winter.

It's also possible that your battery is getting old and weak -- you may want to look at a new battery if the car seems hard to start after sitting overnight.

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  • Same, when I had a car where the lighter was always on I much preferred it to the ones where the ignition had to be on (or in Acc). I never had negative effects leaving a charger in there because there wasn't any load on it. And for any times where I had to sit in my car waiting for someone or something, it was great to be able to charge my phone without having to power up a bunch of other stuff.
    – briantist
    Commented Dec 21, 2018 at 4:09
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To build onto @rpmerf 's answer, here is a visualization:

2 Fuse Taps in serial

In this example, let's say you have a SPARE unused Fuse slot, and the ALWAYS ON Cigarette Fuse slot. Depending on your manufacturer's recommended maximum amperage (my Cadillac CTS 2008 supports up to 30 amps in the front panel shared across both spares), you could use two Fuse Tap pigtails connected (like properly crimped) via the red cable, and divert power from the positive HOT SPARE to the negative Cigarette terminal, while inserting 2 total fuses into the top of each pigtail.

But don't forget, if the cigarette lighter's maximum allowed amperage is 20 amps, to use 20 amp fuses, not 30!

Here's another schematic of this possible idea:

Schematic of 2 Fuse Tap pigtails

It should work because the HOT from the cigarette connects to nothing and no longer powers anything constantly. And the HOT from the spare travels via 2 fuses and the red cable to power the cigarette.

Don't forget: It's super important to get the polarity correct! In this diagram, I purposely REVERSED one of the pigtails (so I don't need to solder any wires into the fuse hole).

Nobody takes responsibility for blown fuses, explosions, toxic fumes, or defragmented zebras!

Edit:

Here's a photo of me successfully carrying my HOT spare to my cigarette lighter:

Joining 2 fuse taps in serial

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I have a suggestion, but I don't know, why not use the world that. Disclaimer: this is only a plan!!!

Step back a bit. If you use another fuse socket for supply the cigar lighter you can overload the socket. And in this case, you should replace the whole car relay-panel.

Why does not switch the built-in cigar lighter socket by a small relay based on the "desired-stated" fuse socket?

DYI Example:

  1. You have #1 fuse socket for cigar lighter, and #2 for e.g. lamps (that automatically switches on at ignition)
  2. You buy a 12-24V relay to control the #1 socket
  3. Put a fuse-tap into the #2 (as everyone uses it), but control the relay with it.

I know, this is a bit complicated, but if a manufacturer creates this stuff in a small box, I think, this can be more useful and safe than currently available stuff.

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I just got my used 2013 Ford focus, and run dashboard camera through the cigaret lighter. Did run tests with battery booster in the trunk, just in case if battery will die on me. Yes, it turns off in about 20-30 mins, but if you have weak batteries won't suggest doing it.

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