Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Charging light

My charging light is starting to blink while I am driving...goes on & off during idle, but more worrisome...blinks on occasionally during driving at speed. Belt is tight...does this mean the Alternator is going bad?
Bob Dougherty


I would assume you have checked that all of the terminals are clean to the alternator, and fuse box are well connected. After that I would recommend you check out Paul Hunts 'spanner' pages for a few test proceedures.


Larry C. '74 B/GT & '69 midget
Larry C '69 Midget

Check the bulb isn't falling out of it's socket too! You never know, you might get lucky and it might just be loose.
Simon Jansen

Does sound like the alternator is on its way out, or possibly a loose connection between it and the solenoid. The charge light has two wires and isn't grounded in the socket like the other bulbs are so being loose in the socket won't be a cause. Mind you, it could be on all the time but it *is* loose and you can only see it when it lines up with the socket ...

Connect a voltmeter to any brown, white or green in the engine compartment or behind the dash and monitor the voltage *except* at the alternator. It should normally be at about 14.5v, dropping towards 13v as more load and less revs are applied. If it drops below 12.8v, and particularly if it flips between that and 14.5v, then you are losing the charge.

Connect it to the brown at the alternator and monitor again. If it drops on the brown then it is the alternator, if not then it is the connections.

If all the previous tests show a relatively stable 14v or so, but the light is still blinking on and off, monitor the brown/yellow. If that is going above or below 14v (either will cause the bulb to glow) then again it is the alternator, possibly the voltage regulator.

Could be nothing more than worn or sticky brushes or slip-rings.
Paul Hunt

This thread was discussed between 20/10/2008 and 21/10/2008

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.