Change of polarity

[C.J.]

Electrics have always totally baffled me, brought to earth by aliens I reckon. Either that or it's witchcraft.

So, this popular mod of changing from positive to negative earth.
What's it all about, why do it, and if it's so good, why wasn't it like that in the first place?

Please educate this seemingly dopey earthling.

[GeordieDave]

The reason I did it was to fit a modern radio and tracker, both needed negative earth. Otherwise I wouldn't have bothered - and didn't for my first 10 years of ownership. If it ain't broke... and all that. I think you have to make the change if you want an alternator too?

Not sure why older cars were positive earth, or why manufacturers made the switch, but I'm sure someone on here will know. I heard something about cathodic action and rust. Maybe wikisomething will know?

[C.J.]

Suspect I'm going to have to do it then, as Miss C.J. will no doubt be wanting a radio with one of these ipod connection thingy wotsits.
I'd personally rather install a nice radiogramme in the boot, so she can play all my old 45's whilst on the move.

Halogen headlamps need fitting too, to replace those current electri candles...xenons even p'raps?

[lambrettalad]

try this post

http://www.mmoc.org.uk/viewtopic.php?f= ... eo#p455625

[John.n]

When using jump leads it is worth checking polarity just incase bumpers or doors of the two cars touch and weld themselves together!
Regards,
John

[bmcecosse]

Just to add - Xenon headlights are completely illegal on a Minor.......... Fit halogen lights if you will, but actually - correctly adjusted sealed beam units are surprisingly effective.

[C.J.]

try this post

http://www.mmoc.org.uk/viewtopic.php?f= ... eo#p455625

Tar for that, but I'm still a bit mystified about the whole subject tbh.

[C.J.]

Just to add - Xenon headlights are completely illegal on a Minor.......... Fit halogen lights if you will, but actually - correctly adjusted sealed beam units are surprisingly effective.

I was joking actually.
Got them on the family car, and am not particulary fussed for 'round town use, but quite good out in the wilds.

[Bazzalucas]

Just out of curiosity, why are Xenons illegal on a Minor? Inquiring Americans want to know!

[bmcecosse]

Can only be fitted to cars with self levelling and headlampwash/wipe - and I don't believe there are approved 7" diameter light units anyway...

[Bazzalucas]

Ah! Thanks. And let me add that while self-leveling makes sense, requiring wipe/wash seems a bit much.

[C.J.]

Can only be fitted to cars with self levelling and headlampwash/wipe - and I don't believe there are approved 7" diameter light units anyway...

Don't think the wipe is legally essential iirc.

Waste of time anyway imo.
Got these xenons on the family car, and the wash facility is only good for shifting wet mud tbh.

[bmcecosse]

Turns out you don't need wipe - but DO need wash......... This all applies to 'real' HID Xenons - and not to 'kid on' xenon filled bulbs in standard headlamps.....

[bmcecosse]

Still mystified? Disconnect the battery - turn it round - reconnect battery. You 'may' need to swap the cable terminals over since the +ve terminal should be slightly larger and may not clamp well on the -ve term of the battery. Swap the connections on the coil - clean the fuel pump and dizzy points. Take a length of wire - from the +ve term of the battery and 'flash'it against the small terminal on the dynamo a couple of times. That should do it - you 'may' need to swap the connections on the back of the fuel gauge - i'm not sure about that.

[C.J.]

Still mystified? Disconnect the battery - turn it round - reconnect battery. You 'may' need to swap the cable terminals over since the +ve terminal should be slightly larger and may not clamp well on the -ve term of the battery. Swap the connections on the coil - clean the fuel pump and dizzy points. Take a length of wire - from the +ve term of the battery and 'flash'it against the small terminal on the dynamo a couple of times. That should do it - you 'may' need to swap the connections on the back of the fuel gauge - i'm not sure about that.

thanks for that, but that wasn't the mystification I was actually referring to, but very handy to know anyway thanks!

No, Im still mystified as to how why, who and when it was decided by manufacturers that negative earth was the way forward?

[lambrettalad]

hi try this

The electrical term "earth" or "ground" is a connection that runs through the entire electrical system. It may or may not be connected literally to the soil. When a system is "negative earth", it means the electrical earth has a negative polarity. Power can then be run back and forth using only one wire carrying the positive polarity. Similarly, electrical signals need only one wire. At the destination, the circuit is completed by connecting the "negative" terminal to earth or ground.

Until the 70s, cars were built with either a positive or negative earth, with popular British vehicles being among the last to be built with positive earth. Negative earth was adopted globally by automobile manufacturers for the sake of standardization. It was the introduction of radios in automobiles that may have seen negative earth automobiles being favoured. It was also thought positive earth vehicles rusted quicker.

The US telephone system also uses a positive ground, after starting out with negative ground. However, the trolley cars in Atlanta, Georgia were causing electrical induction interference, which led to the phone cables literally falling apart. Every kind of solution was tried, but they all failed, until as a last resort the phone company flipped the polarity, and it has stayed this way till the present day.

[bmcecosse]

Blimey...learn something new every day! I know it is a corrosion prevention move - but wasn't aware of the telephone/trolley car link.

[C.J.]

Wow Alex. Thanks!
What a 'things you never knew' but always wanted to' post that was.

Still think electricity was brought here by aliens though mind.