MGB Register Forum

I'm thinking of installing a dual USB port with battery charge reading to my B, have any of you got advice on which one to get and how to wire it up?

The easiest way to do this, although it may not be what you want, is to buy a usb port which plugs into your cigarette lighter socket. They are available with double usb ports.
Additionally you can purchase a battery voltage reader which also plugs into your cigarette lighter socket.

Ian F

My MG hasn't got a cigarette lighter, 1971 model, I guess the technologiy for this wasn't about yet so it'll have to be one that I can wire to the harness.

What I would recommend then is to buy an accessory port - just like a cigarette lighter with a modern politically correct name!

You can then plug all of your accessories into it.

If you make the mistake of connecting up a usb port directly into your electrics you may destroy it. This happened to me when installing a usb into a Land Rover.

Someone with more electrical knowledge will no doubt be able to give you a more technical bit of advice.

Ian F

I agree with Ian, fit an accessory socket - what used to be called a cigarette lighter socket. Simple connection to a 12V supply and an earth. Then buy whatever sort of plugs you want. USB runs at only 5v so don't attempt to connect one directly to your 12v system! The plugs that go in to the lighter socket do the voltage reduction for you.

Just had a look at Vehicle Wiring Products who I have used many times, and they have very neat USB sockets with a built in voltage reduction. Here's a whole page of sockets (https://www.vehiclewiringproducts.co.uk ... gs-sockets). I like this one (https://www.vehiclewiringproducts.co.uk ... ory-socket).

I went for one of these as I wanted tidy panel mounted rather than installing a ciggy lighter socket and an adaptor.
https://www.ebay.co.uk/itm/405968675746 ... 5qVm&pfm=1

Not_Anumber wrote: Tue Sep 09, 2025 1:24 pm I went for one of these as I wanted tidy panel mounted rather than installing a ciggy lighter socket and an adaptor.
https://www.ebay.co.uk/itm/405968675746 ... 5qVm&pfm=1

Where did you wire it to in the car?

Any ignition switched live will feed it. The device itself drops the voltage to the necessary 5 volts for USB.

On the subject of USB in cars; I recently realised there is a limitation with the USB connections provided by many after market audio systems and ANdroid screens. They are ok for a data connection but often dont have sufficient current capability to run a phone with everytyhing enabled. In fact with many of them the current available is so low the phone battery will discharge almost as quickly as though it wasnt connected.
The solution is to cut the red and black wires inside the USB lead so the device is no longer dependent on the stereo for it's power. I used a short USB extension lead for this instead of cutting into an existing USB lead https://www.ebay.co.uk/itm/265332431893

I then used a voltage dropper https://amzn.eu/d/6zMawK7 wired into the car's live and earth to provide the required voltage for USB but at much improved current. Done neatly all the wiring can be hidden other than the one visible lead to the phone.

The voltage dropper can be run from any ignition switched live and its output (yellow and black) wires then connect into the USB lead.

This setup will now supply sufficient current for the phone to run gps, data, bluetooth and wifi etc without the phone battery going flat on long trips.