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MG MGB Technical - Postive to Negative earth

Hi,
I intend to gaange my car from postive earth to negative.I understand the principle but any comments and tips would be welcome. Will a postive earth rev counter need to be changed?

Thanks and a Happy New Year.
s page

Yes, you will need to modify the rev counter.
These links should help you do it.

http://www.mgexp.com/article/neg-convert.html

http://www.mgexp.com/article/tachometer.html

Herb
Herb Adler

There's a John Twist 'comedy' video...

https://www.youtube.com/watch?v=ddZ0E2Wd6Ic&feature=em-subs_digest
Dave O'Neill 2

You need to take account of any other electronics in the car, like fuel pump, for some years replacements for these were polarity sensitive.

You might also like to have a look at this http://www.mgb-stuff.org.uk/electricstext1.htm#ground
Paul Hunt

And don't forget to change or at least cover over the positive earth label on the face of the tacho so future owners don't get misled.
Paul Walbran

Strongly recommend adding "NEGATIVE EARTH" stickers to the battery cover and front hood support. (burned out an alternator and a set of electronic points when my brother jumped my 67 B)
Bruce Cunha

Negative earth is safer according to my electric guru
Ellis Carlton

"Negative earth is safer according to my electric guru"
Don't know why, other than garage attendants not being aware of the vehicle being positive ground. There is absolutely no difference in operation between the two polarities. Our TD has never been converted from positive ground and I have never had any problem whatsoever. That said, I stand by the car with a club in my hand whenever someone other than me, is changing the battery or doing anything at all with the electrical system. If I see them starting to hook something up incorrectly, after I have emphasized that the vehicle is positive ground, they get their knuckles rapped. Cheers - Dave
D W DuBois

"Don't know why, other than garage attendants not being aware of the vehicle being positive ground."

Ditto.

Those giving written advice often say to 'disconnect the negative battery terminal first' when what they should have written is 'disconnect the earth terminal first'. But then again, how many people don't know how to identify negative or earth terminals anyway? They probably shouldn't be fiddling with a battery anyway. Not long ago a regular contributor to the MGOC magazine said when using jump leads to 'clip the free ends together' when attaching the other end to the first battery. Next month someone complained that they did that and blew up their battery.
Paul Hunt

Paul

Was that who I think it was?
Dave O'Neill 2

My mistake. I should have said positive ground because of maybe tools or something falling across. I have cutoff on TD positive ground since that cuts all off
Ellis Carlton

Ellis - I doesn't matter which side of the battery goes to ground, if you get a wrench between the two you are going to produce large arcs and sparks, usually doing grievous damage to the wiring harness and causing the wrench to go into the incandescent mode. Cheers - Dave
D W DuBois

Dave - probably :o)

A cut-off switch in the earth cable, regardless of whether the battery is connected positive or negative earth, is a marginal benefit over having it in the 12v cable. It means by turning the switch off you can then work on the 12v battery connector safely. But if you are doing that to remove the battery, i.e. will be removing the earth connection anyway, it makes no difference. Fitting one in the earth cable is easier though, access-wise.

But if you mean a wrench falling across the battery posts, having a cut-off switch won't prevent that causing arcs, and incidentally running the risk of blowing up the battery.
Paul Hunt

This thread was discussed between 02/01/2015 and 17/01/2015

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