...may seem like a simple and odd question that one could test (and I plan to), but offhand I'm wondering if the X300 will continue to run if the battery is healthy and fully charged and:

1) Power to the alternator regulator is cut off?

and/or

2) If the alternator itself is not charging/connected?


Older non-computerized and distributor fired cars of old would often continue to run for a good while just on a battery as long as not too many accessories and lighting were on. I think I once drove a car home for a couple miles just on battery and very dim headlights... stumbling the whole way. But I'm curious if the X300 is capable of doing do at all or if so, for how long.

I can easily and quickly test scenario #1 by pulling the fuse in the RH engine fuse block that powers the regulator. #2 is a bit more involved, but also not difficult to test by simply removing the charging wire from the alternator.



This is related to troubleshooting the issues I'm having/referencing in the following threads:


https://www.jaguarforums.com/forum/x...-p13b0-192634/

https://www.jaguarforums.com/forum/x...ctions-194669/

https://www.jaguarforums.com/forum/x...me-use-196614/

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I drove my x300 ~30 miles just on battery when I bought it with lights and blowers on windscreen every 10 minutes for a minute. No problems at all. Battery was still fine and charged enough to start the car when I fitted replacement alternator a week later.
I did have a backup battery in the boot just in case the first one wasn't enough to get me home.
I've also drove through half a meter of water on a few occasions and it can take 20 miles before the alternator dries out and starts to work again.

 

Engine will run until it gets below 11.5 volts or so from what I've heard .

By removing the power to the regulator on that 1 small wire you will lose power generation . That can be seen in your driveway as a voltage with a hand held meter going down as you let it idle and blowers running and such .

A test to do would be to ensure you have power to the regulator to prove the regulator does work and the problem is the power to the regulator . The hand held meter staying up . You can load the alternator down with blowers and such and if the test fails you will be in your driveway .

Regulator would have to heat up under electrical demand / load to see it fail thereby limiting your test travel range .

If you see 14.5 volts or abouts on the large B+ post on the alternator as you alter the load from light to heavy this would prove the regulator is regulating the alternator to keep up with the demand . Getting that power to the battery as it's the distribution point is something related to the mid - car terminals you're checking out .

 

Thanks, I suspected that the car should run on healthy and charged battery alone.

That makes me wonder if this indeed is completely an electrical problem specifically associated with the alternator and charging, but I'll wait on that judgement until I complete the other electrical troubleshooting. I don't want to wander too far afield at this point. After all, when this all started, the alternator clearly was not charging when the car was idling normally.

I'm still going to check:

1) The regulator power wiring from the RH engine fuse box to alternator is in good shape.

2) The charging cabling from alternator to battery including the four junctions (starter, firewall, under rear seat, battery terminal) along the path.

3) Connector at alternator that provides power to the regulator and connectivity for the voltage dash gauge.

4) And I'll check the various other incidental grounds along the way that I can find.


If the problem persists after that, we're going to have to look elsewhere and probably re-examine the symptoms.

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Might have to remove the alternator again after that and put it on the spin up machine and get a reading as a new alternator is not always good off the shelf . I know you've done it before . We had a saying at work " I can't fix S%&# with bad parts " .

Is your negative battery cable in good shape ?

 

Here's the thing... during this last incident on Monday I kept an eyeball on the volt gauge and it stayed rock solid the entire drive. So even if the alternator completely failed, I shouldn't have had the car stumble and die like it did at idle after driving it for 10 minutes because the battery was fully charged (I charged it the night before) based on the conversation above.

So if it is electrical, I'm not convinced anymore that it is alternator related. And yep, this is my second new alternator after the original was diagnosed as not charging by Autozone. Note, this was by testing at the battery, so again it could be the wiring in between the alternator and battery.

Of course, the main positive cable and its connections are still suspect.

Yep, the positive and negative battery cables in the trunk are clean, like new and tight.

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Since the gauge off the other regulator monitor wire shows good and no charge light ( ? ) does the battery have a intermittent open cell as it warms up and expands ? You would have to knock on the battery with a 2 X 4 around the side if not warmed up to simulate this .

 

Interesting test, I'll keep that in mind.

The battery is brand new though. I replaced it as part of this troubleshooting because the old battery was several years old and got stressed through all the charge/discharging.