I want to add powered USB ports to my car to charge various devices with. My plan is to order these USB soldering connectors fuse holders, 3amp fuses, and some wire.

Now I would find a hot wire somewhere before the dash panel, probably a connection from the 12v cigarette lighter, splice wire from there and run wire to fuse holder, which would hold the 3amp fuse, then wire from the fuse holder to the positive lead on the usb soldering connector, and then a ground from the positive lead to a ground mount somewhere in the car. Then simply put the soldering connector in the dash panel somehow.

I would use one 3amp fuse for a pair of ports, and would have 2 pairs, one in the front and one in the back.

Now my questions are, what size wire should I use for this? Do I need any diodes or anything? Do I have the right fuse size? Should I have a resistor or anything of that nature? Does everything else sound like it should work fine? I'd also imagine that the current would already be DC since it's using the car battery, but I could be wrong.

I don't have a ton of knowledge on electronics but I feel like I have enough to get this simple task done. That's why I want make sure every thing sounds right and don't end up messing something up.


  • Buy this instead so you don't blow up your electronics.
    – Matt Young
    Dec 5, 2015 at 19:45
  • I'm looking to do something more permanent and looks nicer. That's why I want to do this. Please explain why you believe I would blow up my electronics?
    – AllanJ
    Dec 5, 2015 at 20:11
  • Because what you plan to do is power a usb port with 12 volts... usb is 5V. Bye bye phone.
    – cde
    Dec 5, 2015 at 21:01
  • Which is exactly why I asked if I need anything else.
    – AllanJ
    Dec 5, 2015 at 21:17

1 Answer 1


Wiring a usb port directly to a cars 12V wire will fry a usb device. Never do this. If you want to do this, you should go with a 12v to 5V regulator. Preferably, a dedicated car usb charger. Then you have a few options.

  • You can remove from its case, and attach it directly where you want the usb port to go.
  • You can use a usb extension cable, either normal or one meant for mounting in a car mod.
  • You can desolder and extend the usb port as needed.

The second option is simplest. They tend to have mounting clips, and no soldering needed. Various styles too.

enter image description here enter image description here

For any modern phone, you want to extend all four usb pins from a dedicated charger, or they will refuse to charge at high speed or at all. Here is a simplified explanation on why using just a 12v to 5v charger wouldn't work well.

For wiring from your chosen 12V wore to the usb charger, 18 AWG wire would be best. The extra fuse is not necessary, as the cigarette lighter circuit should already be fused at a reasonable 10 Amps.

Frankly I found that slim usb chargers that flush mount to a cigarette outlet to be the easiest. Unless you need the outlet for something or its in a weird place...

  • Thanks. So I need a regular. And that's really it right? I understand what you're saying about taking apart a USB charger, but I'm wondering if this, amazon.com/KEEDOX®-Converter-Power-Supply-Module/dp/… , would be a cheaper option instead of buying 4 chargers I could buy two of these, one for a pair. Correct?
    – AllanJ
    Dec 5, 2015 at 21:34
  • Or even this ebay.com/ulk/itm/251734856189 may be an even better option. What do you think? Thanks again.
    – AllanJ
    Dec 5, 2015 at 21:38
  • The problem with the first is that there is no circuitry for newer phones to determine what speed to charge at. If your lucky, they will charge at regular 500mA speed, which some phones will actually discharge or take hours to charge. Others like the iPhone won't even charge, saying unauthorized accessory. Look at the link I provided. The second one, maybe?
    – cde
    Dec 5, 2015 at 21:47
  • Do you happen to know if there is a way to tell if a certain product has d+ and d- connections that regulate the amount of power the device accepts? Or is it kind of just a guessing game?
    – AllanJ
    Dec 5, 2015 at 21:59
  • 1
    Got it. Well I think I'm probably just going to go with that second one I linked from eBay. So it seems like that's all I really need. Just connect that to the 12v wire from the back of the cig lighter, and mount the USB port. I may need some extra wire, but I think that's it. Thanks for the help, hopefully that will work, if not I'll look for something else, thankfully it's only $2 so I wouldn't be out to much if it doesn't.
    – AllanJ
    Dec 5, 2015 at 22:08

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