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MG MGB Technical - alternator warning light

my alt. lite gets brighter as my revs go up. checked voltage at brown heavy wire at fuse block and am getting about 14 volts. at idle it is slightly under 13 volts. adding a load (headlights) at rpm has little or no effect.charging seems about right except for red lite. have suspicion of diode block problems. would appreciate any ideas...
ljc coker

Replace the Lucas with a Delco or Bosch nuff said....
Alyn

LJC,
Replaced my alternator after the regulator went bad. Considered replacing just the regulator, but the alternator was cheap enough. Replaced it with a Lucas, and it works fine. Not sure what other kinds of ideas you may be interested in...this is the only one I have.
Fred Doyen

Your post could not be more timely. My 79 Mgb did the same thing two weeks ago. Converted to the Delco-Remy unit and problem solved.

Let us know how this item turns out

cheers

Gary :>{D
gnhansen

I think its safe to say that once per week, someone who reads this board will have a Lucas alternator failure. Mine died a month ago, and due in no small part to this board, I replaced it with the Saturn Delco unit. Thanks everyone!
Jeff Schlemmer

LJC,

Knowing the year of your MGB would be helpful, but let me suggest several details which may assist you in determining the fault of your alternator.

Service your battery -- half of all electrical problems in the car come from bad (loose/corroded) battery terminals. Remove the clamps! Wire brush the posts, wire brush the inside of the clamps. Resecure and tighten very snugly! Replace the battery clamps if you cannot get yours to tighten.

Ensure that the connexions of the WHITE wires between the ignition switch and the main wiring loom are clean and tight.

How have you fared with this?

John Twist
University Motors Ltd

John H Twist

first of all, thanks everybody for the suggestions-- i was returning home from missouri when i started getting my red lite--it came on momentarily then went off,but before i got home it was on more than it was off. i opened up the alt. & thought i found the problem..one short brush(the one that runs on the outer dia.)..i replaced that but not the problem. called AUTO ZONE and picked one up for $60.00.(lifetime warranty). it works fine..i have a little over 210000 miles on vehicle ('73 mod.) and this is first problem with lucas alt. outside of brushes! thanks again!! P.S. john, i chkd connections as you suggested & i think all was o k. it's showing about 13.8 to 14.0 volts at about 2000 revs. with about .2v drop with headlites on.
ljc coker

lgc,
If at the brown wires you are getting 14 volts then your alternator is working just fine. At idle 13 volts again would be a normal reading. Just replacing your LUCAS (bad word I guess) with a bosch, delco etc will not solve the problem. They will only provide the same voltage. If the alternator light is on then something is not right. Normal charge voltage (insert name of alternator) is about 14 volts. A well charged battery will provide about 12.5 to 13 volts. How did you measure these readings? A multimeter with a charged battery will show about 13 volts. During starting will go down to 12 volts or below. It could be the regulator is not right, allowing a full charge IE 14 volts no matter what the state of the battery. I do not belive that any other alternator will just bolt in on the same mounts.

HTH

Ron
Ron Smith

This thread was discussed between 11/08/2005 and 14/08/2005

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