positive/negative earth- how to tell

[MartinLowe]

Hi
first time of posting, will be picking a up Minor on thursday, and have been wondering how to tell whether the car is positive or negative earth. is it as simple as the braided cable attached to the + terminal on the battery or am I missing something out. For example this is a photo of the engine bay of the car in question As far as I can tell it has a dynamo rather than an alternator

[bmcecosse]

Yes - it's as simple as that.........

[mike.perry]

It looks like a 948cc engine and yes it is a dynamo.

[mogbob]

Martin
The car's engine bay looks great.If the rest of the car is as good ,you've choosen well.
From the picture it looks as though the pipe ( Breather hose ) from the rocker box to the carb has a nasty split ( ? ) That being the case it is probably a good idea to replace fairly soon.( ESM charge £2.35 for the part, so shouldn't break the Bank )

One more day to go !! Have fun with it, safe motoring.

Bob

[MartinLowe]

From the picture it looks as though the pipe ( Breather hose ) from the rocker box to the carb has a nasty split

is that the pipe that rises from the top of the engine and then bends to the right? what is it's function?
Will be picking up the car tomorrow so will check
The rest of the car is very nice as well, I will be taking plenty of pics!!

[bmcecosse]

The pipe sprays oily fumes all over the outer surface of the air filter element - and clogs it up - a really great idea. The later carbs have a suction tube on the side so the fumes are drawn directly into the engine - avoiding the filter. Much better! It is possible to modify the early car filter mounting plate - putting a hole in the front face and fitting the pipe in there - thus avoiding the filter!

[MartinLowe]

sounds like a good scheme, I'll get it done asap

[mogbob]

Thanks Roy for providing Martin with the info yesterday.
Didn't get onto the Forum yesterday, busy putting doors and wings back on my pal's Morris Minor.He's got it booked in at the paint shop at the end of the month.So a busy time with last minute bits and pieces.

Bob

[Bit of Both]

I have just purchased a 1960 Morris Minor. As it came without a batterry in the car and there are no markings on the batterry terminals, I was wondering how one determine whether the car is positive or negativeley earthed? Thanks

[Alec]

Hello Bit of Both,

if it has a dynamo it is almost certainly positive earth, if it has an alternator then it will be negative earth. It is easy to change the polarity on a dynamo but not with an alternator.

Alec

[bmcecosse]

The +ve battery post is larger than the -ve post - so look carefully at the battery connections on the car and try to decide if one looks a wee bit bigger than the other. As Alec says - if it has an alternator it WILL be -ve earth and connecting it wrongly can cause expensive damage. With a dynamo - it could be either polarity - would have been +ve earth, but could have been swapped. Other clue is - if it has a modern wireless set fitted - it will almost certainly be -ve earth.

[andygill]

I'm thinking of fitting a cigarette lighter.

Is there anything I can buy that I can use to test it to ensure I don't 'fry' anything.

Thanks
Andy

[Trickydicky]

Hi,
The best option would be to fit an inline fuse of a lower rating than the device you are powering. The fuse will then blow first, but are you using it as a cigarette lighter or will it be used to power a Sat Nav or other device?

[andygill]

Hi,
The best option would be to fit an inline fuse of a lower rating than the device you are powering. The fuse will then blow first, but are you using it as a cigarette lighter or will it be used to power a Sat Nav or other device?

Thanks for your reply. I want to use it for my ipod/iphone ? hence I don't want to fry it.

[Alec]

Hello Andy,

you will need to ensure that the polarity is correct; most electronic devices cannot be connected to reverse polarity without damage.
I don't understand Dicky's advice of using a fuse of a lower rating than the device it powers, that ensures the fuse will blow for no good reason. Fuses protect the cable feeding a circuit which in turn is sized to the load it feeds so will be rated a higher current than the device takes.

Alec

[andygill]

Hello Andy,

you will need to ensure that the polarity is correct; most electronic devices cannot be connected to reverse polarity without damage.
I don't understand Dicky's advice of using a fuse of a lower rating than the device it powers, that ensures the fuse will blow for no good reason. Fuses protect the cable feeding a circuit which in turn is sized to the load it feeds so will be rated a higher current than the device takes.

Alec

Any chance someone can look at the photos below and see if it is +ve earth



This cable is connected to the +ve and goes into the engine etc




This cable is on the -ve and simply goes to the body nof car.

[Alec]

Hello Andy,

that makes your car negative earth as the battery negative is connected to the body.

Alec

[bmcecosse]

That battery clamp is not really holding the battery down........ It should be fitted to the top front edge of the battery - but make sure it can't short out against the battery +ve terminal......

[xpress]

yes, that metal piece needs to be wedged into the top edge of the battery and the rods are tight, "pulling" the battery into the front bulkhead.