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MG MGB Technical - Lost (almost) all electrical power

On the way home last night, with my 79 B, the engine suddenly died, lights all went out, could not restart. Everything is dead except for the horn, clock, interior & trunk light. Fuses all look good, battery connections are all tight & there are 12 volts going to the starter, yet the starter will not turn. Any suggestions?

Thanks. Allan, Upstate NY, USA
A. Steckenberg

Check the large brown wire(s) onto the solenoid + check engine earth cable connections.

R
richard boobier

The horn, clock, interior & trunk light are all on the 'purple' circuit, so you have still got power on the brown to the fuse box, but no other circuits. If you check a wiring diagram for your year and model, it should give you a clue as to where the power is being lost.

Not being too familiar with late model Bs, I'm not sure how many circuits are relayed, particularly on North American models.

Dave O'Neill 2

Don't trust the fuses by sight. Measure them to see if they are really fine and also make sure the contacts on the fuse box are nice and clean too.
Simon Jansen

As Dave says if the horns an interior lights still work (including while turning the lights on and trying to crank) then the problem isn't at the battery or solenoid.

Neither is it with any fuses, as the ignition and headlights (at least) aren't fused. A double-brown comes up from the solenoid to a special 4-way connector, then from there one wire splits off to the fusebox and starter relay, and the other wire feeds everything else. Check all the connections at that 4-way connector i.e. both wires both sides. The first stopping-off point for the 'everything else' wire is the 3-way multi-plug for the light switch, which is used as a tee for the other item in that brown circuit which is the ignition switch. As the lights aren't working check both browns are secure in the pin of that connector, i.e. one of them (the feed) isn't hanging loose.

Paul Hunt 2010

This thread was discussed between 02/05/2010 and 03/05/2010

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