Positive Earth and modern gadgetry..

[gs.davies]

If I preserve the Positive Earth system on my car but fit cigarette lighters isolated and wired as per negative earth, is there any danger in frying the circuitry of things like iPhones and the like should the device's casing come into contact with the car bodywork?

[woodypup59]

Much easier to change to -ve earth.

Saves any heartache.

[gs.davies]

Yes, it probably is easier, but does the use of anything modern inside the car preclude keeping it positive?

[olddave]

Shouldn't be a problem if well insulated. But as Woodypup says .............

[Peter Laidler]

Woodypup has given the real answer of course. But in response to to your Q about keeping it positive AND using isolated modern stuff, I'd say no but I'm not an electronics man! BUT ask anyone that's gone down this route and fried their tacho or radio or a part of the wiring loom and they'll say take woody's advice. Remember Murphys law of physics and Darwins law of natural selection. If something can go wrong, it WILL. Keep the car and its equipment ONE or the OTHER but NEVER a mix.

[gs.davies]

I suppose it makes sense. In any case I suspect my old battery leads will want replacing being nearly 60 years old

Negative it is. So much for being positive this year

[woodypup59]

Changed one of mine to -ve when the fuel pump died.

The replacement pump was only available as -ve earth.

I simply swapped the battery leads, and started the engine.

If the ign warning light had stayed on, I'd have flashed a wire across the two dynamo terminals to repolarise it.

[agricola]

In the early 70s I was involved with the switch of positive earth vehicles to negative in particular tractors most of which didnt have radios.
All the dynamo systems accepted the change with no issues, as did wipers heaters etc. At the same time I fitted an llac alternator to my +ve earth S and it was -ve earth so it was changed too. The big push for it was we were told that battery pillar corrosion would be reduced on the earth pillar. Thinking back it seems to me that was right although I think the use of copper slip etc had an influence.
I have a 53 grey Fergusson which is -ve earth and has been for the fast 50 years same electrics etc

[gs.davies]

In the early 70s I was involved with the switch of positive earth vehicles to negative in particular tractors most of which didnt have radios.
All the dynamo systems accepted the change with no issues, as did wipers heaters etc. At the same time I fitted an llac alternator to my +ve earth S and it was -ve earth so it was changed too. The big push for it was we were told that battery pillar corrosion would be reduced on the earth pillar. Thinking back it seems to me that was right although I think the use of copper slip etc had an influence.
I have a 53 grey Fergusson which is -ve earth and has been for the fast 50 years same electrics etc

I have heard of this corrosion on the positive side thing before - maybe that's why my car rotted out so spectacularly...

[snoopy64]

If I preserve the Positive Earth system on my car but fit cigarette lighters isolated and wired as per negative earth, is there any danger in frying the circuitry of things like iPhones and the like should the device's casing come into contact with the car bodywork?

I guess it depends where you are planning on putting the power socket... i have my speaker and a usb socket mounted in a kick board under the rear seat not much chance of it shorting if something broke..its in mdf and surrounded in carpet. Optimize Auto made me a half board so I can still have the obligatory wicker basket on the other side! MK2 black interior so you don't even really know its there

[gs.davies]

Probably nothing more exotic than a cigarette lighter USB socket to keep the phone topped up. It was really a concern over if a metal bodied phone contacted the bodywork whilst plugged in, thus creating a circuit..

[agricola]

What is really important for those people who are not mechanical is to know which is the earth AND
Always remove the earth terminal first when removing a battery and connect the earth terminal last. When I taught students those who ignored you normally tried to to weld spanners to the vehicle, the unlucky odd one where a battery had not been properly vented learnt how explosive hydrogen was....

[hanlminiman]

Woodypup has given the real answer of course. But in response to to your Q about keeping it positive AND using isolated modern stuff, I'd say no but I'm not an electronics man! BUT ask anyone that's gone down this route and fried their tacho or radio or a part of the wiring loom and they'll say take woody's advice. Remember Murphys law of physics and Darwins law of natural selection. If something can go wrong, it WILL. Keep the car and its equipment ONE or the OTHER but NEVER a mix.

Very good advice Peter. Current electrical items are negative earth. Period radios and tachos were negative earth so if you convert "simple is efficient!" Peeps. My period radios include instructions on how to change polarity.

[IslandBlue]

My Mk2 Cooper is still positive earth. I wanted a cigarette lighter socket for satnav, 'phone charger etc. I realised that these are polarity sensitive and rather than try to completely insulate the socket from the bodywork I rewired the socket to make it positive earth which meant some disassembly and some soldering but it was possible and works fine.

Many years before I had wired in a negative earth stereo with a graphic equaliser (remember those) and boost amplifier by insulating them from the bodywork. This worked fine and was very loud, I built some cabinets to fit bass units under the rear seat as well. I gave up in the end though because at any appreciable speed if the music was loud enough to drown out the engine and transmission it made your ears bleed....

[gs.davies]

My Mk2 Cooper is still positive earth. I wanted a cigarette lighter socket for satnav, 'phone charger etc. I realised that these are polarity sensitive and rather than try to completely insulate the socket from the bodywork I rewired the socket to make it positive earth which meant some disassembly and some soldering but it was possible and works fine.

Many years before I had wired in a negative earth stereo with a graphic equaliser (remember those) and boost amplifier by insulating them from the bodywork. This worked fine and was very loud, I built some cabinets to fit bass units under the rear seat as well. I gave up in the end though because at any appreciable speed if the music was loud enough to drown out the engine and transmission it made your ears bleed....

Confused now; you’re saying that rewired the socket to effectively reverse the connections inside to provide for a positive on the pin and negative on the outer which is how it’s be in a negative Earth vehicle?

[850man]

Just make the car negative earth. Its that simple.

[Exminiman]

Just make the car negative earth. Its that simple.

Have to agree, why keep it positive when it so easy to change to negative ?

[IslandBlue]

My Mk2 Cooper is still positive earth. I wanted a cigarette lighter socket for satnav, 'phone charger etc. I realised that these are polarity sensitive and rather than try to completely insulate the socket from the bodywork I rewired the socket to make it positive earth which meant some disassembly and some soldering but it was possible and works fine.

Many years before I had wired in a negative earth stereo with a graphic equaliser (remember those) and boost amplifier by insulating them from the bodywork. This worked fine and was very loud, I built some cabinets to fit bass units under the rear seat as well. I gave up in the end though because at any appreciable speed if the music was loud enough to drown out the engine and transmission it made your ears bleed....

Confused now; you’re saying that rewired the socket to effectively reverse the connections inside to provide for a positive on the pin and negative on the outer which is how it’s be in a negative Earth vehicle?

Correct.

Just make the car negative earth. Its that simple.

Can't argue with that although I'd considered going to negative earth when I got the car in the late 80s but never did mainly because I was worried about the rev counter not working (which could probably be rewired in some way).

Mind you I've now compounded the problem by fitting a positive earth electronic ignition set up - which of course doesn't work with the old rev counter.

Madness I know.