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MG MGB Technical - Battery charging

With the battery under the floor it’s not easy scrabbling about behind the front seats to get easy access to the battery to connect a battery charger especially with the hood up ( I leave the hood up in winter to keep it stretched). I usually charge the battery a couple of times during the winter.Is there a safe way of connecting the charger to the battery under the bonnet. Someone suggested connecting to the fuse box but thought I would check with people whose advice I trust. Thanks
Trevor Harvey

I have fitted one of these https://www.autoelectricsupplies.co.uk/p/battery-lead-junction-box by the pedal box with a short starter-type cable from the battery cable junction on the starter to the box. Not only does this make it easy to charge the battery, but is also handy if a jump start is needed. Just clip the negative lead to any clean engine or body place.
Mike Howlett

Same here but only needed in case of a jump-start or boost charging.

For basic charging you can pick up 12v from the purple circuit (fused always live) at the fusebox, and from 1972 you can use the lighter socket with a male plug on the charger leads as that was connected to the purple circuit from the factory. From 69 to 71 it was on the accessories circuit so the ignition key would need to be in and turned to the first position (accessories, not ignition), but prior to that it was on the brown circuit so key not needed but unfused.

However for any of those if you have a battery cut-off switch it has to be turned on of course ... unless you have a switch with a bypass fuse for clock, radio etc. then that will contribute to battery drain. But if putting a charger on just a couple of times over winter is enough to start the engine when you need it it sounds like you don't have a drain.

I leave my cut-off switches off all the time in the garage, a pal used to but forgot one night and the second photo was the result, which may have been from brown wires round the steering column shorting out. The body looks OK but the car nearest the camera was written off as the interior was totally destroyed with the worst damage round the column and dash. The other one needed a new top and bonnet repaint plus extensive cleaning to get rid of the soot, still not back on the road after five months.






paulh4

Although my car has been fitted with an 18v engine with pre-engaged starter, it still has the original starter solenoid on the inner wing, so I connect my trickle charger to there on the very rare occasion that I think it might need a bit of a charge.
Dave O'Neill 2

Paul, that fire damage looks familiar, when I stripped my car down about 20 years ago the screen and dash was removed it was obvious that at some time previous there had been a fire to the wiring so I fitted a cut off switch accessible just in front of the drivers seat. This is used whenever the car is idle.
I will use the purple wire at the fuse box for charging thanks.
Trevor Harvey

Both mine before they came to me and at least three I have worked on have all had shorts to the white wire at the pump. Not a problem with the car switched off but bad enough, and is why I've fitted fuses in that circuit and strongly recommend them.

The overdrive circuit is also unfused so I have fitted one there as well. Sometimes both are easiest done where the three harnesses join together in the engine bay by the master cylinders. When I had a float puncture in the V8 being together was very handy as I cross-connected them then used the overdrive switch to turn the fuel pump on periodically and briefly so it wasn't pumping out onto the floor all the time.
paulh4

This thread was discussed between 07/03/2025 and 11/03/2025

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