Negative Or Positive Polarity? Avoid Smoking Your Generator!
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Title: Negative Or Positive Polarity? Avoid Smoking Your Generator!
Tip:
In the age of alternators and electronics it is not always easy to deal with the generator-regulator set up on earlier cars and determining the ground setup of the electrical system. On Jaguar, two rules generally apply for determining the polarity (Negative or positive ground- also called negative or positive earth).
If it has a generator it is positive ground and if it has an alternator it is negative ground.
If it has a 4.2 engine it will most likely have an alternator. The 4.2 E-Type in late 1964 and the 4.2 Mark 10 were some of the first to come equipped with alternators. The Sport Saloons (Mark 2 and 3.4, 3.8 ‘S’ types) had generators and were positive earth. The 420 Sport Saloon, introduced for model year 1967, was the first 4.2 engine in a Sport Saloon and first equipped with an alternator.
There may be a few cars that have been changed/ modified from a generator (positive earth) system to an alternator (negative earth) system. Also some cars may have been inadvertently hooked up wrong. To correct the polarity on a ‘generator system’, first make sure the battery is hooked up correctly. Then use a piece of wire and touch one end of the wire to the field terminal of the regulator and momentarily touch the other end of the wire to the regulator battery terminal. The engine should not be running to polarize the generator. Any time a generator is removed for service or replaced it should be ‘polarized’ before startup.
If you have questions about what a generator is, check the repair and owners manuals for your car or check with someone who knows.
the correct procedure for re-polarizing a Generator to Negative Ground can be found at http://www.starautoelectric.com
I did mine (1965 S type) with Mike Martinez’ help, he’s the owner of Star auto Electric, in Monrovia, Calif., who rebuilds Lucas generators, Alternators, etc. (there was an incorrect procedure at the JCNA Technical Library which was quietly corrected after Mike read it and told them it was a dangerous procedure which would smoke the Generator!).
After converting to Negative Ground, my car felt and still feels electrically “peppier”, seems to have more energy, electrically speaking. I would not go back to Positive ground. Also, I wanted consistency with my other Jaguar, a 1984 XJ-6. Don’t want to be thinking “ohh this car is Negative but the other is Positive”. Nahh, give me Negative Ground all around.
Jose
28 Jun 07 at 5:02 pm
Jose,
Thanks for the comment – I’ll check out Mike’s site and let you know what I think.
Moody
9 Jul 07 at 11:24 am