Car battery polarity

That would have been ex-MOD and used to power radio equipment. Such vehicles sat for hours with the engine running, but the landrover engine was never designed to be used like this, so these vehicles quite often had knackered engines.

As others have posted, pre (about ) 1960 or so +ve earth was common / the norm.

I remember my father and brother discussing reversing the polarity of an old car, this must have been around 1964/5. I assume it was a Ford Popular.

People ‘flashed’ the dynamo’ to reverse them - this was pre Alternator. Cars had little if any electronics back then - often not even a radio*- no ECU etc to fry.

• I remember my parents taking a portable radio in the car on long trips and having an aerial wire on the rear parcel shelf. I seem to recall, if you had a ‘proper’ car radio you needed an extra licence. A portable didn’t.

Getting back to your trailer, you may find ( if you have a canbus tow bar interface in the car) it doesn’t ’like’ LED bulbs. Some do, some don’t.

If you have a problem, using bulbs with load resistors to ‘fool’ the system is the usual trick.

In message <v7av4l$2c2mt$ snipped-for-privacy@dont-email.me, at 12:43:16 on Thu, 18 Jul

Mine was fine, although I only kept it for a year. Some may have been as you describe, but others just as likely to be stored for most of their life, awaiting some conflict zone to be sent to.

Even a decade later than that. Positive earth, really began to decline, when alternators became more common.

It was the work of a minute, to simply change the car to negative earth, plus swap the battery round - always assuming there was no electronics on the vehicle.

Many of the early car radios, had a plug on the rear, to set them up for either positive, or negative earth.

I had a valved Motorola, which used low voltage valves - it worked quite well.

Yep - you needed a radio licence, for the radio you used at home, which covered a portable, but if you had one installed in the car, you needed a separate one. I seem to remember if it was in any way attached to the car, that applied, including if powered by the car, or plugged into a car aerial.

ISTR my 1996 Vanden Plas 4L R ( the Rolls engined Princess) was +ve earth and I changed it a few days after I bought it.

It rally has little to do with that. Perhaps a little to do with the advent of the silicon NPN transistor and the growth of car electronics, but even that is not an insurmountable problem. IIRC the alternator thing was not ispo facto an alternator property, simply that all the early diode packs and regulators were made 12v negative earth, so thats the way it all stayed.

Like many things, its simpler to have one standard, but there is no technical reason for that standard whatsoever.

Why do we drive on the Left? half the world does not.

But it is important that people stick to the standard

Upthread I recalled discussion at the time concerning polarity and bodywork corrosion. A brief search turned up a raft of stuff about sacrificial anodes. Whether the polarity change helped or manufacturers coincidentally used better finishing is open.

There's also stuff around that suggests the +ve earth is good if you really use an earth connection as part of the circuit (early telecoms given as an example) but is probably irrelevant for cars which are pretty well insulated from earth (normally).

nib

I was told at the time that it was to reduce the corrosive effects.

There may have been a cost difference that motivated the choice. Car manufacturers will put a lot of effort into making a small cost saving. A preference for using npn transistors could have been such a driving force. John

Didnt f****ng work, did it?

Galvanizing, better paint techniques, design improvements reducing road dirt trapping etc. probably coincided with the polarity change.

You must remember early Minis rusting around the headlights and cills. Ford Cortinas not much better...

Didn't change when the polarity changed either

A lot of that was bad handling at the factory, no gloves, bad preparation before painting.

Imposed voltage systems are known as "Cathodic Protection". Typically used to protect underground pipelines from corrosion.

Sacrificial anodes are lumps of an electronegative material such as zinc which when in contact with say, the steel hull of a ship will stop/reduce corrosion to the hull.

Otherwise known as zinc-dipping or galvanising