Thanks very much for the lesson. You sound like you were a fab teacher.

 

I was looking over the workshop manual and noticed the internal regulator of the alternator is a simple linear mode circuit. The complex switching mode operation comes from the ECM. Basically the ECM monitors a variety of electrical and other conditions, and directs the regulator / alternator how to act.

Battery and Charging System - General Information - Charging System
Description and Operation
Vehicles with 2.0L, 2.5L or 3.0L engines

The engine control module (ECM) can switch the voltage regulator between two voltages to optimize the charging of the battery.
The low voltage regulator setting is 13.6 volts and the high voltage regulator setting is 15.3 volts, measured with the generator at 25°C (77°F) and charging at a rate of 5 amps. These values decrease with a rise in temperature or current flow.
The ECM determines the voltage setting of the voltage regulator. The high voltage setting is always selected by the ECM once the vehicle has started. The ECM determines the period of time that the high voltage setting is selected for.
There are three different time periods selected by the ECM which is dependent upon the vehicle conditions when the vehicle is started:
The longest time period is selected if the ECM determines that the vehicle has been 'soaking' for sufficient time to allow the engine coolant temperature (ECT) and the intake air temperature (IAT) to fall within 3°C (37°F) of each other.
The intermediate time period is selected when the ECT and the IAT is below 5°C (41°F).
The shortest time period is the default time and is used to provide a short period of boost charge.
At the end of these time periods the voltage is always set to the low voltage setting to prevent the battery from being overcharged.
The time periods are variable depending upon the temperature and the battery voltage. The target voltage of the battery varies between 14 volts and 15 volts depending upon the ambient temperature and the vehicle operating conditions. Once this target voltage has been achieved, providing the vehicle has been operating for at least the shortest time period, the ECM will reduce the voltage regulator to the minimum setting of 13.6 volts.

That was from page 2081. I'm beginning to think your ECM may be the culprit. But there are a slew of tests that can be done in the Manual.

If you have the ability to check the ECM codes... according to the manual it should be storing them.

I hope that helps.

 

Nice find Hobbs!

That exactly what I was referring to when I posted this earlier;

"All I remember from my times under the hood chasing the fore mentioned cable problem..Is that when the car first starts there was a higher charge voltage for a few minutes, then it would drop to about 13.6v at idle and remain there until the next start cycle....It was describe in a technical manual on this as a means to re-charge the battery quicker after start-up to replenish the battery drain that took place during starting."

 

You were right on! I also noticed that because the ECM plays large in the charging system that any shorts, high wire resistance, or weak connections between the alternator and the ECM will light up the charge indicator.

Again from pg 2081 of the manual:

A fault in the wiring or the connections from the generator to the ECM, will cause a fault code to be generated and stored in the ECM and the charge warning indicator lamp to be displayed in the instrument cluster (IC) after a short time.
The charge warning indicator lamp is operated by the IC after receiving a signal from the ECM through the control area network (CAN).
With the ignition switch in the RUN position the charge warning indicator lamp will be displayed in the IC when the generator is not generating power.
If a fault is detected with the generator a fault code will be generated and stored by the ECM. The charge warning indicator lamp will also be displayed in the IC.

I'm replacing all of the wire, like you did, if I can ever find a mechanic and the cable spec's!

Any ideas on how to locate a qualified Jaguar mechanic, who works under the principles of honor and integrity, I would greatly appreciate the lead or information!!!

 

Thanks all. For now anyway the charge issue has been behaving itself and hopefully will continue so. Thanks all

 

Ok alternator playing up again. Charge light on. When I start car and put lights on the lights are going bright and dull flicking up and down as the voltage increases and decreases. I have read that if I disconnect the smart charge 3 wire plug from the alternator it reverts back to a standard alternator but the charge light will remain lit. When I do remove the 3 wire smart charge plug the alternator does not charge at all so it is of my opinion the alternator is indeed at fault. Anybody have any ideas. I always thought that an alternator needed power to make power so surely disconnecting this plug will cause it to stop charging but forums say otherwise. HELP AHHHHHH !!

Thanks