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Electrical problem

Started by june2017, May 03, 2017, 12:01:44 PM

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I have recently discovered an electrical problem with my '71 MGB.  Shortly after I bought the car 2 years ago, I replaced the alternator ($59 at Autozone), because the red ignition light on the dash would come on intermittently.  When this happens, the radio shuts off (low voltage?) and the engine cuts out, but it comes back within a second or two.  Recently, it has started doing the same thing, and I am wondering if the problem may have been something else.  I don't know much about the electrical systems on these cars.  Does the car have a voltage regulator?  Is there anything else in the charging system which could be causing this kind of problem on an intermittent basis?
Thanks for any suggestions you may have.
Jack Wheeler


This is why British cars have such a bad reliability reputation and we all love Lord Lucas so much.
Yes the car does have a voltage regulator, which is an electronic module board built into the alternator (back side in the black plastic cover behind the connector plug). 
Replacing that is not as easy as taking the old one out and putting a new board in.  No, in typical British fashion, each run had a unique board that may physically fit a different one, but might not work. Or work only for a short time.  It's why so many have turned to swapping in Delco or Autolite alternators to replace the Lucas ones.
Before getting to that point, a few other things to check:
- Make sure the connectors on the alternator are clean and not damaged.  A poor connection can give the same symptoms.
- When was the last time you checked the batteries?  Bad or loose cable connections there could cause issues.  A bad cell or weakened battery as well.
- Trace the alternator wires back to the other connections at the fuse box or starter,  Same scenario.
Once you've checked these and any others you might think of, then start rechecking the alternator itself.  Even if it proves to be the regulator board, better to bring it back to Auto Zone as a unit for replacement.  Better still, chalk the $60 up to a bad choice and get a replacement from an LBC specialist.  Mine cost around $100 from British Miles about 15 years ago and is still going strong. And I've added a more powerful radio, higher cranking amp battery and an electric cooling fan since installation.  Worth every penny.
Hope that helps you.  Keep me posted on what you find.  Hope it's something simple and cheap to fix.
Best regards,
Art Isaacs
Art Isaacs
AMGBA Tech Staff

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