Down to Earth

[Paul Heffernan]

Hi all

I'm guessing this has been done before, but I can't find anything via "Search" So apologies up front!

It's entirely possible that could be dreaming, but I'm fairly certain that I read somewhere that UK cars did not move from Pos earth at the same time as the USA Cars. Also my 1974 (CB) MGB was twin 6V batteries/Generator/Positive earth. I say "was" beacuse I understand that changes where made during the restoration, it's now single 12V/altenator/Neg earth.

So, my plea is, can anyone please point me to a definitive source that clarifies when UK cars moved from Pos to Neg Earth. I am 100% sure that for the USA cars it was 1968, but I'm pretty sure that here in Blighly, we stuck with Pos Earth for a few years longer.

Thanks in advance.

[George Wilder]

Thats the sort of detail to be found in The Original MGB by Clausager - unfortunately I don't have my copy to hand.
George

[Vic Butler]

The reason for changing from positive to negative earth was the alternator. All alternator equipped MGB's started at GHD/N4 onwards. The Rootes Group had cars fitted with positive earth alternators in about 1966 but it was found alternators preferred negative so by end of 1967 most cars were fitted with alternators and negative earth.
However, BMC were slow to introduce it to other cars in the range. Morris Minors, Farina range never had alternators even though the Minor and Morris Oxford soldiered on until 1971. I believe the Mini, 1100 and 1800 range were late in fitting alternators .
The change over started late 1960's and by the early 1970's all cars were fitted with alternators and were negative earth
It appears that the MGB was the first BMC car to have an alternator and negative earth. It wasn't an immediate change to negative earth.
This is how I remember the change over. I've written this from memory

[Ian F]

72 BGT always negative earth! (says so on the sticker on the bonnet slam panel).

Ian F

[Vic Butler]

I had a look in the BMC 1800 workshop manual I've got. Although the spec shows that an 11AC alternator was fitted to Mk2 versions as well as a dynamo , the wiring diagrams show only a dynamo so perhaps alternators were fitted for export only.
My parents had a suffix J reg Morris Minor Traveller in the 1980's and I'm sure that had a dynamo.