MGB Never occurred to me that my '66 would be positive ground. Does the presence of an alternator show that it's been converted?

[Vardaman]

I put a new 12v battery in place of the original dual 6 volts, and have been troubleshooting the electrical system. All seems to be going well, but then I read someplace that these cars were originally positive ground. If it has an alternator, that pretty much proves that either someone converted it, or somebody REALLY didn't know what they were doing. What else might be a sign that it has been converted? What might they have missed?

 

[BobHaskell]

Which way were the 6 volt batteries installed? Negative or positive connected to the chassis?

 

[Vardaman]

Which way were the 6 volt batteries installed? Negative or positive connected to the chassis?

Sadly, I didn't think to look. I just noted which cable was which.

 

[mezy]

Sadly, I didn't think to look. I just noted which cable was which.

If you noted which cable was which,
Which one is connected to ground.
I don't know that any positive earth alternators were ever made, they came along, way after manufacturers went negative earth.

 

[PAUL161]

I think I'm correct on this as I've had both, 1978 MGBs on were Negative ground, before that they were Positive ground systems.

 

[Grantura_MKI]

Any B after 1967 was neg earth and had an alternator fitted.

 

[PAUL161]

My 70 and 72 were both positive grounds. ?? My 78 was negative ground. Again, ??

 

[Joe Reed]

All MKI cars ('62-'67 model years) were equipped with a dynamo (generator) and were positive ground.
All later MGBs ('68-'80) were equipped with an alternator and were negative ground.

 

[Vardaman]

Mine is a '66, so it was originally positive ground with a generator. It has had an alternator retrofitted (it's kind of a kluge, but at least it's not Lucas!!) So my question is, if someone added an alternator to a car that was originally positive ground, would it necessarily have been converted to negative ground?

 

[Grantura_MKI]

Yes.
Would rather have the later Lucas alternator with the built in regular, as it cleans up the wiring a bit.

 

[mezy]

Yes

Mine is a '66, so it was originally positive ground with a generator. It has had an alternator retrofitted (it's kind of a kluge, but at least it's not Lucas!!) So my question is, if someone added an alternator to a car that was originally positive ground, would it necessarily have been converted to negative ground?

It would have had to be converted to neg earth for an alternator

 

[JamesH]

i have NEVER heard of a positive ground alternator, so i would take the presence of an alternator as proof that the car is negative ground.

 

[DrEntropy]

Alternator fitted? Decidedly the car was changed to negative ground. Converted our '64 to negative earth back in '05 when doing the rebuild. Put an alternator in a couple years ago, a Lucas unit. Replaced the external regulator with the faux box sold by one of the regular suppliers, it reroutes the wiring internally, just to approximate original appearance. Also swapped out the cover with the Lucas one just for S&G. Looks like the "original." Also put the "IMPORTANT: This vehicle is negative earth" decal on the under-hood panel.

 

[Mickey Richaud]

i have NEVER heard of a positive ground alternator, so i would take the presence of an alternator as proof that the car is negative ground.

The unicorn is real! We're considering one for the Healey we're restoring, as we've had issue with the generator and voltage regulator. Check it out: > 12-Volt, 1-Wire Alternator, 63 Amp, Positive Ground - The Brillman Company <

 

[NutmegCT]

Vardaman - " It has had an alternator retrofitted (it's kind of a kluge, but at least it's not Lucas!!)"

Following on Mickey's reference to the positive ground alternator, what make/model alternator is on the car now? And could you give some details on the "kluge"?

Tom M.

 

[Vardaman]

Vardaman - " It has had an alternator retrofitted (it's kind of a kluge, but at least it's not Lucas!!)"

Following on Mickey's reference to the positive ground alternator, what make/model alternator is on the car now? And could you give some details on the "kluge"?

Tom M.

I really hadn't looked, but had assumed that it was something more modern. In fact, it IS a Lucas with the internal regulator. The "kluge" is that it uses the original alternator mounting bracket with a long bolt and a thin sleeve forming the rear brace.

 

[DrEntropy]

I believe we got this "extended" bracket through Moss, but don't remember for certain.

 

[Vardaman]

I'll have to track one of those down.

 

[Grantura_MKI]

Moss number 460-315
Lists for $25.99

 

[Vardaman]

Moss number 460-315
Lists for $25.99

Great. Thanks. I'll include it on my next order.