positive to negative earth

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burnham28
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positive to negative earth

Postby burnham28 » Wed May 22, 2019 2:07 pm

Have just been to have a radio fitted to my minor only to be told that my car is positive earth and they need my car to be negative earth. As far as I understand to switch over I have to turn the battery round so that the terminals are on the opposite sides then change the coil leads, the fuel pump leads and the solenoid leads. Is this correct? If not can someone advise me what to do. Help would be appreciated.
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geoberni
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Re: positive to negative earth

Postby geoberni » Wed May 22, 2019 2:24 pm

Basil the 1955 series II

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burnham28
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Re: positive to negative earth

Postby burnham28 » Wed May 22, 2019 4:04 pm

Thanks for that have been into the previous posts and it looks like an easy swap. There is no mention of changing the solenoid leads or the fuel pump. Do these have to be done?
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geoberni
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Re: positive to negative earth

Postby geoberni » Wed May 22, 2019 6:44 pm

Not that I'm aware of; both are simple items that should not be polarity sensitive.

You haven't said what age/model the car is. The really early ones i.e. MM and perhaps early Series II (?) need a few tweaks to things like fuel gauge, but from the way you're talking, I'm guessing it's not that old.

What about your Points, are they conventional? They'll need cleaning and resetting. I read somewhere that the Fuel Pump points need the same, not because they won't work, but it's the fact that the minute spark at the breaking contacts is now jumping the other direction, so the transfer of material from one side of the points to the other will now reverse.

Although the car will run with the Coil wiring unchanged, you should really swap the White and White/Black connections on the Coil. If you don't, then essentially the spark are jumping from the Plug body to the centre electrode, instead of the other way around. A very inefficient way to do it!

Warning - if you have electronic Points, that's a problem as they are polarity sensitive, so don't change anything until you've come back here!

I think that's about it, unless anyone else has something to add.
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cv01jw
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Re: positive to negative earth

Postby cv01jw » Thu May 23, 2019 7:52 pm

Slightly hijacking this thread, but could people please confirm my thoughts that my car is now negative earth - noticed when I took the battery off to charge and realised that the -ve terminal connects to the bulkhead. Picture below:

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les
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Re: positive to negative earth

Postby les » Thu May 23, 2019 9:17 pm

A vehicle with the battery negative terminal going to an earth point is considered to be negatively earthed. The bulkhead/ bodywork is an earth point. I believe the procedure to effect the change can involve some form of ‘flashing’ over on the dynamo terminals but presumably that’s been sorted when the change to negative earth was made, whenever.


geoberni
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Re: positive to negative earth

Postby geoberni » Fri May 24, 2019 10:58 am

Well, from the photo, I've no idea, because we can't see the markings :wink: .
I'm a little surprised, since my battery is mounted with the terminals towards the retailing bar. One of the traditional issues with swapping it around, is turning the battery 180 degrees so the leads reach, and that usually the posts/lugs are a slightly different size.

So it looks like someone has got a battery with the lugs the other way around, such that it will still fit the original way in the car, if you get what I mean.
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As Les said, if the Post with the "-VE" is connected to the bodywork, then it's Negative Ground.

Might be worth checking to see if they swapped the coil connections. I've had Basil 2 years and I only recently realised, despite having been working on the Ignition System, that the Coil White and White/Black cables were still the original way around (White going to coil -ve connection), hence my Spark at the plug wasn't correct, i.e. it was jumping outer to the centre electrode, not centre to outer as it should.
I've read that this can cause the spark to be up to 50% weaker.
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mobylette
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Re: positive to negative earth

Postby mobylette » Fri May 24, 2019 2:46 pm

Looks like you have left a roll of insulating tape under the radiator..

geoberni
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Re: positive to negative earth

Postby geoberni » Fri May 24, 2019 3:35 pm

mobylette wrote:
Fri May 24, 2019 2:46 pm
Looks like you have left a roll of insulating tape under the radiator..
Old photo, but well spotted :D I wondered where that went... :lol:
Basil the 1955 series II

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