Positive or negative earth
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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...
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#9
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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,
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Ken
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,
![Icon Toast](https://www.jaguarforums.com/forum/images/smilies/icon_toast.gif)
Ken
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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.
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.
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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
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.
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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
Note: The smaller post on the battery is negative!!! Cables fit or don't. Clue????
Carl
Carl