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MG MGB Technical - New wiring harness & alternator question

Hello All,
I'm installing a new wiring harness in my '68 B and have small issue with the alternator connectors. My old harness had a black plug with 2 wires, the new harness has 4 individual wires.

The Bentley manual wiring diagram matches my harness. In stripping the old harness back, 2 wires were capped, looks like it's been that way for years.

The 2 un-connected wires are the large black and the small brown/green.

My question is, should I just connect large brown and small brown/yellow (as it was) or hook them all up??

I have a photo attached.

Thanks in advance! David

David Steverson

Originally your car had an external voltage regulator. It probably has been converted to an internally regulated alternator and doesn't use the two extea wires, connect only the two wires in the plug to the alternator.

Clifton
Clifton Gordon

The harness should also have five wires which would originally have gone to the external regulator that Clifton mentions - brown, brown/green, brown/black, brown/yellow and black.

The brown must be carefully turned back and insulated as under normal circumstances it will be always hot and unfused.

Ditto the black as it is at ground potential and must not come into contact with anything else.

Brown/black (ignition warning light) and brown/yellow (alternator IND terminal) must be connected together (if they aren't already), if they are not the alternator won't charge as it should. These must also be carefully insulated and prevented from coming into contact with anything else.

Brown/green is less of an issue as it will be disconnected at both ends, but should still be taped back out of the way.

Paul Hunt 2

I still have the external voltage regulator on the car, it was wired up, but had duct tape over a busted cover. I wonder if it had gone bad? I just (3 days ago) ordered a new one.

I notice the Victoria British alternator part number is the same for all years of MGB. So, will this alternator work with my new voltage regulator?

Thanks! David
David Steverson

The VB alternator will not require or work with the external regulator as the regulator is built in to the alternator. If you really want to keep the external regulator you may need to have an original alt rebuilt.
John H

OK, so I get a little confused on electrical stuff sometimes.

I should:
1) Connect the 2 wires (large brown, small brow/yellow) to the alternator.

2) Do as Paul says with the wires that would have connected to the external regulator.

3) Send my new external regulator back whan it arrives.

Does that sound right??

Thanks! David
David Steverson

David,

yes, you are right with your thouhts. The alternator of your car has a built in regulator, so the big brown wire and the brown/yellow one must be connected, noththing else as Paul allredy mentioned.
You can not add a second exterial regulator to your installation as it is an internal modular part of your type of alternator allredy as common on all cars today.
You should not worry about anything might be wrong with this kind of installation, you simply run the more modern style alternator in your setup.

Ralph
Ralph

I'm not sure this applies to your car, but some owners that have converted to internally regulated alternators use the external regulator as a sort of connecting block. The external is not needed anymore, but it either looks more original or is easier to wire up. Since yours was ducttaped, I doubt if the reasoning was concours originality.
Tom

All,
Thank you very much for your comments. Last night I noticed Moss has some applicable alternator conversion instructions in the catalog.

I also found a higher amp alternator on EBay with a wiring harness conversion connector for 5 wire setup like mine. That setup is about $100 but may be a good alternative.

Has anyone gone that route?

Regards, David
David Steverson

Speaking personally it would be $100 spent vs a little time making connections, if I already had a good alternator.

If you use the original external regulator as a connector block you would need to gut it or disconnect its internals from the connections first.
Paul Hunt 2

Good point Paul. After watching a Top Gear episode last night, I could use that $100 towards a deposit on a Ferrari 599.
David
David Steverson

Speaking of Top Gear, did you see the 'worlds best road trip' from Davos to Stelvio? I've long had an ambition to do that. Top Gear made me even more determined, and this week I get the Shell V-zine and they do they same trip!
Paul Hunt 2

Yes I saw that one Paul. Awesome drive, that. We're a bit behind on Top Gear episodes here in the US, so I download from a website and stay pretty much up to date.

I had the Christmas special Doctor Who by Dec. 26th that way.

David
David Steverson

This thread was discussed between 08/01/2008 and 11/01/2008

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