MGB & GT Forum

Looks like my '70 B needs a new alternator (most likely). Battery is completely dead and car will not keep running once jumper cables are disconnected. Alternator light never goes out while it is running. Assuming a new alternator is the solution, does anyone have recommendations about getting a rebuilt original one vs getting one of the new Lucas ones? As far as I can tell, the main difference is that you need a wiring harness adaptor for the new one because the original has a five-plug harness vs. three on the new ones. Any advice would be appreciated.

Few choices depending what you want, do you want the original look, more electrical power, peace of mind :
rebuilt the alternator (part from brown&gammons)
renew the alternator with lucas or rebuilt by bosch (moss, victoria british, ebay, brown&gammons)
gm alternator

Multiple threads about the issue of changing the alternator.

http://www.mgexp.com/article/alternator-lucas-delco.html

http://www.mgexp.com/phorum/read.php?1,3171782,3171782#msg-3171782

http://www.mgexp.com/phorum/read.php?1,3189066,3189066#msg-3189066

Five or six years I rebuilt the alternator which was already 36 years old. Last year, I replaced with brand new lucas alternator.

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1977 MGB Red 'Victoria' and 2018 Jaguar XE 'Meghan'
All Classics:
Married, 2 children, MG MGB May to December, Jaguar the rest of the year.

Will,

I bought a new high output Lucas unit a few years back from the MG owners club out of the U.K. I don't remember having to change the plug on my 70 maybe I did. Regardless it hasn't given me any problems.

IF you need one quickly, I'd just order a reman. I bought one from Amazon about two months ago and it works just fine so far. Price couldn't be beat ($70 or so) and two day free shipping was included. That said, I kept the original one as I will take it just down the road to Fondy electric and have it rebuilt to keep on the shelf "just in case".

Be sure it's indeed your alternator, not a shorted out battery...

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

Will,

I would venture to guess that all you need is a new battery. Your alternator is trying to charge a dead battery which will not hold a charge.

Put in a new battery and then test with a voltage meter while the car is running. If it's around 13.8 volts, then your alternator is doing it's job.

If you want, you could test the dead battery just to make sure it's really dead. One way is with a battery charger. If it does not hold a charge, well, it's caput. You can also test with a volt meter.

David

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74 Damask Red BGT
Davesmg@outlook.com

Basically remove the battery; put it on charger for 1 hour. If the voltage is increasing, charge for another hour, and continue to so until you got 13.8V.
Disconnect the charger, wait the next day the voltage should stay > 13.5V.

If the voltage never increases and the end result is below 12.5V the battery has one or two dead cell. Renew the battery, charge it before installation is highly recommanded.

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1977 MGB Red 'Victoria' and 2018 Jaguar XE 'Meghan'
All Classics:
Married, 2 children, MG MGB May to December, Jaguar the rest of the year.

Well, got a new battery. Alternator light stays on bright when car is running. Took alternator to local recommended alternator shop, and they say it tests fine. Trying to do some reading here to see what the next step is, but mainly just getting confused at this point. Any recommendations on next steps?

Thanks,

Will

Charge the battery
Then start the car and test the output from the alternator at the alternator and again at the battery.
If the alternator is plugged in and the lights on its not charging.

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A couple of years ago a friend of mine got a '70 MGB alternator from O'Reilly Auto Parts in 36 hours. IIRC, it was about $50.

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T. Keith Vezina
British Motoring Club New Orleans
1976 MGB, 1976 MGB Trailer & 1978 MGB V8

When you install the new alternator DO NOT TEST IT BY REMOVING THE CONNECTIONS TO THE BATTERY! We used to do this in the 60's and 70's but it will blow out the new solid state voltage regulator contained in the alternator. I learned the hard way

If you have still got the alternator with the 5 wire setup and its external regulator it maybe worthwhile to change to the simpler 2 wire setup anyhow*). There is no need to take the external regulator out, you only have to connect the thick spade(s) on a 3 wire alternator to the single thick brown wire connecting to the startermotor and its post for the thick batteryline coming from the + battery post. The small spade connection has to go the warning lamp (yellow brown, thinner wire). All the other wires can stay loose from the old setup after this conversion....

I bought me an aftermarket Lucas 17ACR, but slightly heavier 18ACR are also available at moderate prices. Best solution is buying one with the proper pully attached, so the rotational speed is correct. Other MGE members go for non-MG/Lucas type alternators, but be aware you need to check which wires go where and that the pully on those alternatives have the right diametre

*) PS My first MG garage mechanic did this change from a 5 to a 2 wire connection for me, later I connected BOTH thick spades to the same brown wire inside a standard connector myself...
Not so difficult to convert from one system to the another as long as you do NOT let the engine run with the thick spade unconnected, because the diode pack will blow up on overvoltage



Edited 2 time(s). Last edit at 2016-10-05 12:48 PM by Donthuis.

If it was not charging with a new battery and the alternator tested good, why didn't the alternator shop suggest a fix?

They did suggest checking the current on light in various states.