When I bought my 87 and started the long drive home I noticed the volt meter was showing low voltage. I stopped at Lowe's and bought a nice digital multimeter and confirmed voltage was correct with engine off and also with engine running. Took the dashboard out yesterday for my new woodwork and tested the volt meter. You can see in the photo below the difference between XJ6 guage reading and the true voltage (at the battery with engine off). Also, the guage climbs up to this reading very slowly. Like maybe 60 seconds with a lot of tapping on the glass.

The next photo shows the back with what looks like a little adjusting shaft. It doesn't seem to turn. Anyone know if that is supposed to be an adjustment knob? Any other suggestions? Thanks for your help.

 

Second photo didn't seem to post. Here it is

 

those gauges are always like that, curiously, in my '65 S type they are a lot more accurate.

I guess what you mean by "adjusting" is to calibrate?

 

If I am not mistaken, that adjustment(if it is) will allow you to zero the volt gauge.
My car suffers with the same issue, but once accelerate or I am driving the car the gauge reads correctly. I will just live with it until somebody comes up with a fix.

 

That IS the calibration adjustment, yes. No idea why it won't turn. Try harder; if you break it, replacements are cheap and easy to come by

As for the lazy operation, well, every Ser III I've owned or driven had a lazy voltmeter...both Lucas and Veglia gauges. Weird.

Cheers
DD

 

Doug, you are a genius. That little shaft on the back of the volt guage adjusted the volt reading just like you said. For others that want to adjust (calibrate) theirs, counter-clockwise raises the volt reading and clockwise lowers the reading. And it is very sensitive, a slight twist changes the reading by a couple volts.

Jeff

 

Hmm.
I've never had trouble with Nix's volt meter, if anything it reads a couple volts high which given her age surprised me a little.. However, I've never had Any electrical trouble with that car.

It was obvious when I got into the dash and under the console that a Lot of work had been done, but if the snake doesn't bite you, you never know it was there. I'm thinking the PO, at the time of Restoversion also had all the electrics fixed.

That almost makes up for all the things he Lied about. Almost.
(';')

 

Elinor, that is why one never buys a car sight unseen, most car sellers lie, misrepresent, distort. There are always exceptions.

When I decided to buy a classic S type, I flew to Oakland CA. to see it in person. I just did not believe the pictures I was sent. Turned out the owner was a famous shipping broker from World War 2 fame, with posters of himself and President Eisenhower in his office, for having helped in the war effort in the Pacific. I had to eat my doubts for this man was an honest war hero in his 80's. The car was pristine as he described it and it brought me back to Tennessee 2,900 miles away. Rest in Peace Ted Rausch.

 

I'm reviving this helpful thread regarding Voltmeters/battery gauge to ask a couple of questions. I know the voltmeters are notoriously "lazy" and take some time to register a reading. But my '87 has been never registered accurately, always showing about 11 volts while idling or driving although a voltage meter in the cigar lighter shows 13.5-14V and when I check directly at the battery while idling I get a reading over 13V. I replaced the alternator and the wiring from it to the starter and to the firewall post in the last year. I'm in the process of swapping in new bulbs for the all the gauges and decided to finally address the faulty voltmeter.

When bench testing it with a spare battery, is it as simple as attaching pos and neg on the battery to the + and ground on the gauge? Because I'm not getting a reading at all. I also tried grounding the case of the gauge but still no reading. The needle is not bent, it just doesn't move. So maybe I fried it when I took it out or when trying to test it.

 

Yes


My experience is these volt meters need to see 13+ volts before they respond at all. Your spare battery, even if fully charged, is probably about 12.5-12.7 volts

Cheers
DD

 

Thank you Doug, that makes sense. My spare battery was reading about 12.5 when I was trying to test the gauge. I've cleaned the connections and I'll try testing it in the car again with engine running then try to calibrate it.

 

Doug…is there not a fine “exciter” wire that sometimes comes loose from the alternator, the purpose which is to get that gauge moving more quickly? Or am I inventing this?

 

mine is also lazy registering but if I tap on the glass the needle moves to the 13 volt mark.

I remember this started happening when I changed the alternator from the original Lucas to John's Cars' GMAlt kit. I have never been satisfied with that GM alternator. I just didn't want to repeat that job but maybe one day I will get fed up enough to install the V12 alternator.

 

The exciter wires kick starts, so to speak, the alternator. When your ignition light extinguishes the alternator is charging.

The exciter wire has no direct bearing on the voltmeter itself

Cheers
DD