Why Do These Cars Tend To Have Reversed Polarity Headlight Circuit?

[aido]

OK quite a few folk on here are getting caught out with aftermarket HID kits as they don't work unless you manually change the polarity in the connector by either removing the pins and swapping around in the connector that comes with the kit or alternatively remove the plastic connector that holds it in place allowing you to reverse it that way.

Why is it that these cars have the circuit the wrong way around to other vehicles, ie positive and negative (or is it 12v and earth) are switched around?

I've just had a quick look on the net as I didn't get why standard halogens work but from what I've seen these don't care about the polarity and will work either way - which is why the problem (HIDs not working) only manifests itself with aftermarket HID kits.

Anyone got any idea why not all the manufacturers follow the same way of working or even seem to change it across vehicles with the same connections?!

May be an idea stickying a thread like this for people to see when they've got HID problems as it's a fairly common problem people get!

[Rob]

A halogen or any other type of bulb that uses a filament is just a piece of wire and when the electricity passes thru it, it gets hot and that produces the light - makes no difference to the piece of wire which way the electricity is going throught - its just a bit of wire.

maybe its not the car but the kits? cheap mass produced items from the far east, other explanations are maybe european/uS cars have he polarity swapped ? who knows

[aido]

From what I read on the kits mate it's like you say - factory makes a million kits, sells them all, then the sellers can't be arsed looking into what polarity the cars are and swapping them accordingly and that's when you get into this situation.

Not sure which manufacturer does which but saw a lot of Hondas with the same problem - maybe it's a Jap thing like they like to reverse the steering wheel stalks around as well!

[Boxbrownie]

Don't forget up until the 60's our cars had positive earth systems........if you bought a newer radio or wanted to fit an alternator in place of a dynamo later in the vehicles life you had to "reverse polarity" the item to get it to work. Maybe the Japs just never got out of the habit? :D

I must admit when I had problems with my HID kit it never even crossed my mind the polarity would be reversed.....oh well you live and learn....in my case twice over :winky:

[Boxbrownie]

- maybe it's a Jap thing like they like to reverse the steering wheel stalks around as well!

Thats another point.....don't forget all our vehicles used to have the indicator stalk on the right of the column back then, until we went all "german" and put them on the left side to match the rest of european manufacturers, that was back in the 60/70's too......showing my age now

[aido]

PMSL - I'm just 30 so that's all new to me :P

It's strange actually as my IS was indicator on the left but I'm sure my Aristo is on the right - although I can't remember - I just know it's the exact opposite of what my IS was and what the BMW is my mam's got

I'm forever putting the bloody wipers on when I switch between them!

Guess the Japs actually switch for different markets then so even on an RHD car in JDM territory indicator stalk is on the right, but on the same car destined for Euroland it's on the left - must be a pain in the arse at the factory that!

[Steviewevie]

Yeah British cars always used to have indicators on the right. To me that was more logical, e.g. you could change gear with your left hand and whilst steering with your right flick the indicator. European cars (that were engineered for LHD) always had the indicators on the left. After a while most of our cars changed to fall in line with the continent, but Japanese cars stuck to having the indicators on the right for a while. I actually expected my IS200 to have the indicators on the right still (being Japanese), but it looks like most/all have now fallen in line with having them on the "wrong" side.

Good question about the HID connections, I'm pretty sure you always end up having to plug them in the "wrong" way round on the IS200.

[aido]

The first set I had worked the way they were shipped, then it was the second ones that we had to reverse I think? I'm half tempted to buy a set for my fogs and see what happens there - but luckily I don't know what sort it needs (and don't want to know otherwise I'll be skint )

I do prefer having the indicator stalk on the right as you can drive one handed with your arm on the window and still use them, not like when they're on the left as you are constantly moving about pressing the buttons