'93 XJS 4.0
When I start the car the volt meter sets around 8-9 volts. As the car warms up the voltage will eventually after a couple of minutes reach 13-14 volts. Voltage regulator or Alternator?

 

dancer308,

...or just gauge?

Try putting a voltmeter across your battery terminals and look at it as the car is started and run as a better indication of how much current your alternator is pushing, before you condemn anything

Paul

 

Agree. Probably just a slow to react guage.


I made a patch cord for my VOM some time ago. I can plug it into the cigar lighter.
Volts in real time under various RPM and load conditions. Exonerated my alternator and convicted my battery.


All is now just hunky dory.


Carl

 

My factory gauge does the same. I also use a three pack of gauges and the voltage comes immediately.

 

Thanks all. Will measure volts across battery at startup.

 

It's not quite that simple, you need to know what voltage you are looking for.

A Lead Acid battery is dead when the open terminal voltage reads 12.00, and depending on what type of battery is fully charged 12.70 to 12.85, although can read up to 13.5 after charging.

So based on this your car would not start if the actual voltage was 9 volts.

If your battery is fully charged the alternator voltage will be lower somewhere around 13.2 to 13.8 volts, if the battery is charging the voltage could be up to 14.2 volts.

This is how I would check this.

Measure the voltage across the battery before starting the car. I would expect somewhere just over 12.3 with the battery connected. (EDITED FOR TYPO on the voltage)

Start the car and leave it for a minute or so, the alternator needs time to excite and commence charging. I would expect voltage to be 13.8 to 14.2.

If these are all in the ball park. Remember multimeters especially cheap ones can read a little high or low. I would then look at the Instrument cluster. My first job would be to clean all the ground connections from the cluster to the body. Remove the screw from the body and use sand paper to remove ALL paint, rust corrosion etc. Screw them back in using star washers between the terminal and the panel/body, you can then seal this with seam sealer and a small brush.

Hope this helps

 

Checked voltage at battery, over 12v. Started car, gauge read 8V, voltmeter read 13+V. Will check all grounds on instrument cluster.


Thanks

 

My XJS volt gauge sits on the peg at 9 vts. Moves a little with turn signals when engaged. Checked alternator by disengaging battery while engine running. Engine continued to run. Fourteen + at battery when engine running. Suspect bad gauge. But found that lights won't switch off at switch until until the car is keyed off. That sounds like bad ground???
What ground and where? Your brilliance gratefully solicited.
An after thought. Jaguar Electric Manual shows a direct white wire connection between Volt Gauge an alternator
As I finished the after thought I know the answer. There are two different problems. I know the answer to the gauge problem but not the light switch. Do you know the answers?

 

Generally not considered a good idea

Quite possible


What year and engine? Over the years there were a few iterations of charging and headlight circuits

Cheers
DD

 

This is a BIG NO NO in a fuel injected car as the battery acts as a spike suppressor and disconnecting it can cause ECU failure due to the noise spikes an alternator generates.

The only way to check an alternator is either measure the voltage, should be around the 14V mark or measure the current with a DC clamp.

 

Doug and Warjon. Both right should not have used old technology on 1993 six cyl. even for the ten seconds test.
Haven't pull the dash, but feel the Volt gauge problem is a high resistant short at the dash plug. Reason? Volt gauge flickers in unison with the turn signal. Will let you know. The headlight switch is another matter. Think that is from Chinese HID lights that I plan to remove. They will not focus properly because of the double lens in the facelift model. After removal and return to an incandescent or LED bulb I think the problem will go away.
Thanks for your input; it is always appreciated!

 

Carl ,LOL,LOL,, Hunky Dory ,dont hear that much anymore!!

must be our generation!

 

The Voltage gauge flickering with the turn signal is a classic indication of a bad ground.

You're correct with the high resistance joint. Pull all earth terminals clean the metal at the mount and terminal, when you re-secure them use STAR washers between the metal and first terminal, if they are in an area where moisture could be an issue cover the whole thing in seam sealer this will prevent further corrosion.

 

Warren
I agree with you on the importance of good grounds. I don't think I'll have to check ALL grounds. The gauge does directly to the alternator through a ten? finger plug. I think the problem is at that plug. Still got to pull the dash to confirm and repair.

PS Have visited your country twice. Circumnavigate the continent once. Wonderful people and great nation

 

Battery Condition Indicator is now providing voltage readings. It was as stated a high resistance short at the dashboard "B" plug. Used a pencil eraser to burnish the contacts
and make the repair.
The headlight problem resolved itself. So all in all it was a good day!