Classic cars forum & vehicle restoration.

giles · Joined: 11 Jan 2009 Posts: 34

I just got a 1962 Super Snipe.

Mine is set up to be negative earth. When I came to take the battery out, someone had helpfully left a small piece of paper next to the battery terminal saying on it "negative earth".

Does anyone know if these cars were originally positive earth?

Has mine therefore been swapped over?

Giles..

47Jag · Posted: Sun Jan 11, 2009 11:03 pm Post subject:

Giles,

It would have been positive earth originally. The main advantage of going to negative earth is you can fit an alternator and modern hi-fi.

Found these currently on ebay:

http://motors.shop.ebay.co.uk/items/Car-Manuals-Literature__Humber_W0QQ_catrefZ1QQ_flnZ1QQ_sacatZ36085QQ_trksidZp3286Q2ec0Q2em282?_trksid=p3286.c0.m282

Art

Phil - Nottingham · Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham

Check that is been done properly eg Coil and ammeter connections swapped over - both will work the wrong way but ammeter will show charge when its discharging and hot starting or engine smoothness will suffer with the coil
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Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

Did that car not have a permanent magnet wiper motor? If so it will be running backwards (as will any permanent magnet motors, but not wound-field motors). I realise that would only make the wiper blades go forwards and backwards instead of backwords and forwards (as Buzzy Bee would say He. He.), but that can cause the parking switch to fail because of the cam profile. I have met this result on one or two cars which have had the battery polarity reversed.
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giles · Joined: 11 Jan 2009 Posts: 34

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

Not all wipers running backwards fail in the short time. It is just that the parking cam has a much steeper slope on the side it presents to the parking points in that direction, which accelerates the wear.
I may be wrong in thinking yours is a permanent magnet motor. It would not be the first time by a long way! As long as they continue to work -carry on. But if they do fail it might be the first thing to suspect.
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Rick · Site Admin Joined: 27 Apr 2005 Posts: 22447 Location: UK

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giles · Joined: 11 Jan 2009 Posts: 34

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

DO NOT try swapping wires over! Unless the motor body is insulated (which I doubt) you will finish up with a short-circuit!
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

giles · Joined: 11 Jan 2009 Posts: 34

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

My family had about 8 cars converted to negative earth to facilitate the use of negative earth two-way radios. All had wiper motors running backwards. The 'couple' of failures I mentioned are the two out of the eight which eventually failed, but only over a higher than normal average rate of use. All initially ran and parked without problems. If I remember right the motors still ran, but would not park automatically.
Perhaps I have sparked a concern you do not need to worry a about if your motor is new. Especially as the failures I mentioned probably occurred after at least 30,000 miles and the motors had already had already been in use before conversion.
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

47Jag · Posted: Tue Jan 13, 2009 12:45 pm Post subject:

Jim,

Were these cars from the 70s. I had a P reg Mini with a permanant magnet wiper motor. It's easily recognised by having a round body as compared to the usual Lucas square-ish body motor which have field coils.

Art

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

More the late 60s Art. I think the oldest was a G reg. The was an N reg, which would be about 74.

Jim.
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pigtin · Joined: 23 Nov 2007 Posts: 1879 Location: Herne Bay

I seem to recall that in the fifties and early sixties someone decided that a positive earth caused the body to rot quickly. You could even buy 'sacrificial plates' to attach to the body that did all the rusting for it.
I believe this was the reason for many changes in polarity. Or was it just folklore?

Don.
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