Hi all,

Is the car positive or negative earth? I ask because I've found a hidden audio unit and it works with negative earth.

Thanjs

 

It is typically British being a positive earth car...

 

Daim, I do believe you are mistaken. If it is an XJS it is negative earth. Positive earth British cars disappeared in the late 1960s/early 1970s at the latest.
Greg

 

100% negative earthed. Just a quick look at the battery will enlighten you.

 

I always... What... Huh...!?

Wasn't the XJ-S the last car made by Jaguar to be positive earth!?

Oh, well, I stand corrected! Thanks for the correction. I look a right idiot now...

 

Thanks chaps. Negative earth it is.

 

My experience is that any Brit car with an alternator is negative earth. With a generator.....could be either way but usually positive earth.

Cheers
DD

 

That should have woken me up then... I always wondered if Bosch made the altenators different for Jaguar... But as it looks: no!

 

Even our '65 Series1 E-Type (alternator fitted) was clearly marked with Jag factory warning labels that it had negative earth. I believe that our Mk2s, MkXs and S Types were similarly fitted. Even way back in the early 60s, I know of no Jaguar that had positive earth . . . for that, you're delving back into the late 50s with Mk1s, all having generators.

By the 70s, this move from positive to negative earth was so well known and recognized, that aforesaid warning labels were phased out.

Of a later and more poorly understood development - the impact of digital electronics has introduced more confusion. Despite wiring diagrams, we still see people searching around for switched actives (ie +12V or not) when, for a generation now, universal practice has been to use fused actives tied directly to all devices . . . and each switched via earth or ground connections. This is because the multitude of modern switching is now done by logic devices (my 2007 S-Type has over 20 ECMs around the car) and the internal logic switches handle switching at ground potential far more efficiently and reliably.

Cheers,

Ken

 

Jag switched from positive earth in the 3.8 E-Type's to negative earth on 4.2 E-Type's (both Series 1).
That turn was in late 1964 when the 4.2 engine replaced the 3.8; my E-Type is a late 3.8 Series 1 from October 1964 with positive earth. The PO swapped the generator with an alternator, still keeping positive earth (that alternator was designed to work as such). Not very practical, the electrical circuit is not well designed and I always have to keep in mind where the ground is when I plug my battery charger.

 

The last Jaguars with positive earth were the S Type and Mark 2 in 1967. E Types switched in 1965 with the introduction of the 4.2 and alternator, same for the Mark X.

The rule with Jaguars is if it has an alternator it's negative earth, if it has a dynamo it's positive earth. That's the way they were built, many positive earth dynamo cars were converted to negative earth, as I did to my 1964 E Type.

 

Thanks everyone, this is very useful as I did it want to have to buy an adaptor for postive earthed cars.

 

This is what the PO did on my E-Type.
He kept the positive ground for the car but he added an inverter attached on the firewall just to power a more recent radio with negative ground.

 

Circa 49-50, I worked in a full Service Gas station while attending college. Some USA cars were positive ground (earth) and others negative earth (ground). Out boss was very fussy about anyone not making certain as to which was which before charging or swapping batteries !!! We had a gang charger to do slow charges on batteries. We also did limited "road service". Close by. A cart and a freshly charged battery. Push it to the stalled car. Swap in the. loaner. Get the polarity right!!!


Note: The smaller post on the battery is negative!!! Cables fit or don't. Clue????


Carl


Carl