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MG MGB Technical - 67 BGT Wiring Decision

My 67 BGT is being restored with the intent to be a fun driver and no real modifications except the addition of a factory overdrive unit and a radio. Any reason to not use the generator and a new original type harness. I am not concerned about the originality as much as the funtionality and abilty to use a standard type installation. BTW, the radio will be radio....not the boomerthingy the misguided nad soon to deaf use. You know, the radio(BL), knobs and antenna and the ball game....
Does the use of an alternator help? Can I get a stardard 67 harness setup for an alternator?

You can install an alternator without much modification at all. Whether or not you need or want one is open to personal decision. I find the generator more than adequate on both of my MGBs.

Some will complain that the headlights dim when stopped at a traffic light. They might also complain that the turn signals speed up and slow down a bit with engine revs. Same with the heater blower. Personally I don't see how any of that matters at all. It's just the way old cars work. But if these things bother you for whatever reason then an alternator will "correct" them and make your car's charging system that much more modern in performance.

Running all systems at once, meaning headlamps, turn signals, windscreen wipers, heater fan, brake lights and radio, you will definitely be pushing the limits of what the stock generator can handle. I don't have a radio in either of my Bs but I do run all systems simultaneously from time to time. In this situation I measure a slight drain on the system while the brake lights are on and the engine speed low. At speed the car seems to charge just fine.

If you plan to use power hungry items like high powered lights or stereo amps then an alternator might be a good idea. Also keep in mind that to run an alternator you will have to convert the car to negative ground if you haven't already.

Hope this helps!
Steve Simmons

As your car is a GT the most power hungry item you are likely to have is a heated rear window. However, I guess that they are not too common on '67 cars.

I have had both generators(dynamos) and alternators over the years. The generator is easier to fix and when its regulator plays up you just treat it like the fuel pump.
David Witham

I recently converted my 67 BGT to an alternator, but only because the dynamo had seized and I had an alternator from my 70 BGT on the shelf. It took about an hour once I had the required wires etc. Good clear instructions on
No difficulties at all. Need an alternator, a length of brown thick wire, a few connectors, a new fan belt, a mounting bracket for the alternator and a few nuts and bolts.

I found that with everything on in the rain my wipers were really struggling. If I switched the blower off then the wiper were OK. The alternator sorted this issue.

67 BGT
I D Cameron

If your car is positive ground, convert it to negative ground. Go with an alternator. You can get a Bosch alternator with a lifetime warranty for less than $70-. If you feel the need to replace the wiring, look at the wiring diagrams for late '60s or early '70s B and order a wiring harness that will better suit your needs. Wiring diagrams are available at click on stock schematics. or may even customize a wiring harness for you to allow for headlight relays and radio wiring.

On the most part I haven't found anything wrong with the original wiring. Usually all that's needed is the connectors to be cleaned or replaced.

With an alternator you'll even have enough juice to use a heated rear window.

Derek Nicholson

Finding a heated read window is the hard part! I've been looking for some time.
Steve Simmons


I also have a 67 GT. Sorry no heated window in the 67 (well perhaps in the Special). My car came with Neg ground conversion ( a near must in my book if not just to prevent shorting out the system by hooking it up wrong or jumping the batter wrong (been there done that).

Couple of reasons I stuck with the alternator. Replacement is just an auto parts shop away. A number of different alternators will fit the B. Not as easy with a generator. Break down with a generator failure and you will be stuck until you find a rebuild shop. Power output is better so if you want to add, say a driving light, you have the power.

With the Moss rear alternator bracket, installation is very easy. Wiring is actually easy and totally reversable if you want. No special harnes needed depending on what alternator you add. I use the lucas with two blades. I left my voltage regulator in, primarily because I did not like the empty space it left when I took it out.

Instruction sites will walk you through it.
BEC Cunha

In an Illinois winter you may be asking a lot of a generator equipped car particularly if you find yourself sitting in traffic with the lights and heater on. An alternator conversion is relatively inexpensive and quite simple, and if you decide that original appearance is important you can buy alternators built in generator look alike casings. These units are very pricy though.

Rich McKIe

HRW was available on GTs from 1966, standard on UK cars from Aug 72.
Paul Hunt 2

Thanks for the thoughts. Interestingly, my 67 BGT had a heated rear window originally but somewhere along the hard life this car had, it was removed. As these cars are not particularly rare, I am satisfied to be without. I won't be out in the snow and ice if I can help it. My restored 67 roadster with the dynamo has performed well for the last 7 years for me with all of the little dynamo reminders that Steve mentioned. Now, if I could put an A/C unit(even aftermarket) in this BGT, THEN I would be very happy! Ralph


Where was the switch for the window on the factory installed ones (steel dash)?
BEC Cunha


On my 70 BGT the heated screen switch was just below the heater controls on a small tab. It can be seen in the last pic on

However, I don't know if the heated rear screen was original equipment for the car or whether it was added later.

67 BGT
I D Cameron

Where it was an option and there was no centre console it was probably fitted to a supplementary panel (like Iain's). US 67 cars had it on the centre console between the cigar lighter and hazard switch. On UK 72 cars they were to the left of the cigar lighter, the hazard switch being to the right. In any event UK cars kept the tin dash until the 77 model year.
Paul Hunt 2

67 US cars didn't have a hazard switch. Maybe 68?
Steve Simmons

"67 US cars didn't have a hazard switch. Maybe 68?"

That is correct - '68 was the year US federal law mandated hazard flashers.
Dan Masters

Strictly the Mk11 produced from December 67, 'model year' practice didn't start until Nov 68 for the 69 model year.
Paul Hunt 2

New Heated Rear Window glass is available from Moss. I bought one last year.
Mike Howlett

True Paul. Just for the fun of argument, a GT built in 12/67 probably would not have been sold until 1/68! Especially a US-bound car! Of course I could be completely mistaken about that. :)
Steve Simmons

The HRW switch on a 1970 GT is a pull switch in the left hand hole of the five. HRW is pretty useless though even with plenty of juice.


It *is* where power for the HRW is taken off the green supply which most years were. I have added a relay to my 75 V8 to send fused brown power to the HRW instead of green and the difference in performance is significant. I have also heard of people installing the relay at the back of the car and taking a fused brown supply direct off the battery for even more effectiveness. Other bad connections in the 12v and earth connections will also reduce effectivenes.

Like many other aspects of the MGB, when they are working *properly* they are really quite effective, although I would never expect them to be as effective as a modern car. Having said that I drove my son's 1999 BMW M Coupe from London to Birmingham just a couple of nights ago and found that I needed the temperature control at about 90% for comfort even though the external temperature was plus 10 degrees C. In either my roadster or V8 it would probably have been at 30% or 40%
Paul Hunt 2

This thread was discussed between 03/01/2007 and 12/01/2007

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