Alternator and Negative Earth

[Cannon]

Hi All,

Slowly progressing on Matilda but am still plodding along with the electrics.

The car has been starting OK & running with the charge light on & then it goes out when running.

However the battery has died & will not charge again via a charger which got me wondering if polarities are correct.

I assumed it was a Neg ETH as that's how the battery was installed when I got it.

That battery was dead too.

So I just had a look at the alternator & Noticed that the black wire which disappears through the firewall presumably to the charge light is not connected to the body of the alternator & that the red wire that goes to the battery is attached to the terminal but insulated from the body of the alternator by a rubber washer.

Here's a Pic. Does this look right for a Neg Eth vehicle?

[JDNSW]

The main lead, with the yellow sleeve on it is connected to the B+ terminal. The fact that the terminal is labelled B+ is sufficient to confirm that the alternator is negative earth.

I have never seen a positive earth alternator, but I think they do actually exist, although as far as I know they have never been fitted to any car sold in this country.

John

[bee utey]

That is an extremely common Bosch negative earth alternator, probably off a later 70's Holden or similar. It might pay you to replace the regulator unit, held on with only two screws and an internal wire, and they're pretty cheap too.

Example:

Original Bosch Alternator Voltage Regulator 9190067005 Early Free Post | eBay

[Cannon]

Thanks

So the leads are on the right spots then?

[John H]

I would replace the regulator and whilst you are at it make sure to clean the slip rings(with very fine wet and dry or similar,ensuring a smooth finish.Any scratches/marks will cause the brushes to wear quickly) as these can glaze over creating an open circuit.

[bee utey]

Thanks

So the leads are on the right spots then?

Of course they are. B+ stands for battery positive. The "negative earth" part of the alternator happens due to it being bolted firmly to the engine block via its brackets, which in turn is earthed to the battery negative via various earth straps. If your alternator mounting is loose or corroded it won't earth properly therefore not allow it to charge the battery. Same for all the other earth straps.

[Cannon]

Cool, now I know what B+ stands for

Just for interest, what does D+ stand for?

[bee utey]

...Just for interest, what does D+ stand for?

I was going to say "NFI", then I though a daft explanation may be better, like "DasLichtenbulbenPositif" then I took myself to Mr Google and found this extremely useful Bosch terminal guide:

Bosch Terminal Designations

where it suggests "dynamo positive" as the preferred answer.

[Cannon]

Good onya.

Thanks mate