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MG MGB Technical - 12v socket.

hi all.
i want to fit a 12v cigar lighter socket under the dash on my MGC. i have a live wire spare that was connected to the radio which i no longer want in the car . it works when ignition switched on or in the auxiliary position. i want to put an inline fuse in the live feed. what rating fuse should be used.

thanks bob.
bob taylor

Depends what you plan on using it for. If as a lighter then they take quite a bit of current, much less if it's for sat-nav etc. For battery charging it'll be in between. For the former then you are probably looking at 17 amp rated 35 amp blow as for the later system that came off the purple fuse in the fusebox. The fuse is to protect the wiring, not the device being connected, so as long as you keep to the standard gauge that would be fine. Other than that 5A or 10A should be fine.
paulh4

Here's a clue. I bought a multi-socket thing for the cigarette lighter so that I could plug in sat-nav and car-camera at the same time. It has a 5 amp fuse in it's plug. It works fine with both gadgets working, but when I plugged the electric tyre pump that came with my VW it blew the 5A fuse. So as Paul said, for most things 5A should be fine. If you intend to use somehting a touch more powerful go for 10A.
Mike Howlett

hi all,
can i connect to live on back of ignition switch. then can i use it for trickle charger over winter.but its mainly for sat nav and phone.
many thanks bob.
bob taylor

Sounds like you should get an auto electrician or at least someone who knows what they are looking at to advise / do the job. Could easily end up with a burnt loom or incinerated car.
A J Dee

Bob, having looked at the MGB wiring diagrams from this website:

http://www.advanceautowire.com/mgb.pdf

All the cars with a cigar lighter, take the feed from the Purple circuit from the fusebox, that connects directly to the Brown circuit via the fuse to the battery. American MGC's had a cigar lighter by the look of it, but it is not shown on the UK MGC diagram. So that is the best place to wire your cigar lighter.

Suggest you also fit a slightly lower rated inline fuse in the cigar lighter circuit if you are only going to use it for low power consumption devices and to trickle charge the battery. As Paul Hunt has said, 5 or 10 amp should be fine.

Andy
Andy Robinson

thanks all.
bob taylor

The purple circuit was suggested earlier. Simpler to connect direct to the ignition switch accessories circuit, but that has two drawbacks.

1: It isn't fused so you would need one in your cigar lighter circuit.

2: More importantly it would need the key to be in and turned to the accessories position, not ideal when using it for a charger even in the garage, I suggest.

By 'trickle charger' do you mean the old-fashioned type? Or the more modern conditioning/maintenance type? You can leave the latter permanently connected, but not the former. But unless you have something continually powered like an alarm you should be able to leave the car at least two months and start it without a problem. Clocks and radio memory circuits will be fine. If you DO have an alarm then fit a battery cut-off switch, then you have a safety device as well as an alternative immobiliser. I have them on all three of mine, even the roadster with no standing loads at all.
paulh4

hi paul.
all i want this for is sat nav and phone really. i have a later type solar charger which i want to use over the winter. the bentley wiring diagram shows the brown circuit on fuse box but i believe it to be the same circuit on ignition switch. is this correct. bob.
bob taylor

Yes Bob, the brown at the ignition switch, and the lighting switch, is the same circuit as the brown at the fusebox.

The reason for going to the fusebox is to use the purple circuit, which is already fused as well as always live. I don't have MGC diagrams but during the production period of that car MGBs didn't have the purple circuit coming into the cabin for the map or courtesy light, that wasn't until the 1971 model year.
paulh4

many thanks paul
bob taylor

This thread was discussed between 06/11/2017 and 09/11/2017

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