Alternator or engine grounds...where to search first?

My US version 85 XJS HE v12 has developed a bit of an issue at night. The volt meter has never showed anything above about 13 volts since I replaced the alternator several tears ago. Admittedly, I dont drive much at night…but I have noticed a lower than average volt meter at night when I have the headlights on. This past weekend, it was at night, headlights on and humid enough to close the windows and run the AC. At a stoplight the voltmeter dropped very low…and the car developed a slight engine idle stumble that went away as soon as I pulled away from the stop and the RPMs went back up.

So i figure I need to start by checking all alternator connections and belts ( replaced at time of alternator). But I suspect that all engine grounds need to be checked.

Can anyone point me to the location of " usual suspect" ground locations.

Thanks in advance.

Cheers

Gary

you could make a temporary ground from the engine to the body with a fairly heavy wire maybe # 10 braided and crimp and solder some eye ends to it…find two bolts to put it under (bolts that won’t disturb anything if you loosen them) and test to see if that makes a difference…check your battery voltage and alternator output…

Are you sure it’s a bad ground and not a bad triac?

Lovell,

I can’t rule anything out yet…trying to gather as much info before i get to the car to make my time as useful as possible.

I can read voltage easy enough…but I have no understanding of a triac or how to test.

My basic understanding…is alternators don’t put out as much at idle…and don’t become truly effective until higher rpms…but that is word of mouth. But it makes sense to me.

Any useful tips on testing the alternator in the car? I don’t enjoy the thought of removing it for bench testing.

Cheers

Gary

Someone will correct me if I have it wrong…

Triads cut in windings as you need them as the electrical load modulates.

I went for about a month before I found out one leg of the three was no good. Symptoms…car would run flawlessly during the day, but, when nighttime driving commenced, I was running off the battery because the alternator could not supply the load. Lights with AC going caught it. Just lights, no issue.

Lovell,

Thanks for that info…that sure sounds like my problem. I will put higher suspicion on the alternator while still checking and improving grounds.

Cheers

Gary

Add a ground regardless Garry.
It will not harm and it will definitely help even if your existing ground is fine.

With a multi-meter check your Alt’s output voltage, with A/C, Lights, fans at Hi and all auxiliaries on.
If bellow 12.5v your battery is not charging.
The diodes inside are easy to replace and don’t cost much, it could fix the problem but not for sure…
On my Mercedes had the same problem, changed brushes & rectifier and lasted only a couple of months. Apparently the they were not the cause but the effect.

When I changed the Alt of my 86 V12 I got this one (after much research):

ALT319, 120A - LAND ROVER 90/110 3.5 V8 (1983 to 1990)
http://www.vehiclepartsdatabase.com/vehicles/allprivateroadvehicles/landrover/90110/35v8/na/11224/alternators/rollingcomponents/alt319

It’s a direct fit, same pulley, internal fan, it only needs a couple of washers on the tensioner, and costs less than $100.
Its on my car for more than eight months now, and the Voltmeter never goes bellow 13V.
On the third picture, on the left, you can see my added ground strap.

Best,
Aristides

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As electricaly challenged, I go for the sound ground approach. I do have qualms with multiple ground paths.

  1. First fantasy. The car’s chassis plays no part in the ground paths. All lodsa re insulated and have two wires. On hot from the battery + and the other back back to battery -.

  2. Not quite as radical. Whenever a load has a black -, it goes to the point that battery - is attached to the chassis.

  3. My conversion ahs a series of relays. I created a mount bar that expands on the original Jaguar unit in the center of the cowl. All but one ground wires go to a ground bus immediately along side. That bus is grounded on the wing, along with the - from the battery.

  4. I’m very proud of the patch cord that I made up. It connects my VOM to the car via the cigar lighter outlet. I can read volts in real time under various loads and rpm’s.

  5. The meter in the dash does not measure, it merely indicates and slowly at that.

  6. I delight in needles that wiggle or numerals that vary. As opposed to the stabilized versions
    Created so as not to worry the folks…

Carl

In general, if engine RPM is above 1500 and voltage is not between 13.6V and 14.4V, the alternator is not working properly.

I actually have no problem with the chassis serving as the ground path. The problems are generally not with the chassis itself but rather with the ground connections to the chassis. There’s one little sheet metal screw behind the starter relay that caused me some trouble. The big ground strap between engine, subframe and chassis is routinely misconnected or left entirely unconnected by mechs working in the area. The ground strap from the battery in the trunk to a bolt on the trunk floor has been known to get all corroded and electrically iffy.

At my local hardware store I found a box full of bronze fasteners, including bronze split-ring lock washers. I bought a bunch and used them to upgrade some electrical connections along with some stainless steel screws and nuts. It seemed to help considerably, but I didn’t keep the car long enough after that to confirm it provided reliable long-term connections.

I also made a plug in voltmeter for the cigar lighter…doesnt anyone make one commercially

Buying a cigar lighter plug and connecting your VOM to it couldn’t be much simpler. What might be an interesting product, though, would be a voltmeter on a cigar lighter plug so you plug it into your cigar lighter and there’s a voltmeter right where the cigar lighter knob used to be. Of course, I dunno anyone who would care other than British car owners.

Now there’s an interesting little project! Kirbert, aren’t you supposed to be filling sand-bags right about now? Seriously- Good Luck when Michael comes ashore to you and family.
Dave.

Here is an interesting little gadget:
USB for yar phones, voltmeter, different colors and all!
https://www.ebay.co.uk/itm/Car-Charger-Dual-USB-3-1A-Adapter-Cigarette-Lighter-LED-Voltmeter-For-Cell-Phone/112855378267?hash=item1a46b4695b:m:mcDRbFj0MHDPk9KhrwMOnJw

Filled and placed 18 sand bags. No damage to house, but dozens of trees down all around the house. Can’t even get to my trash hole. No power, probably won’t be restored for weeks. Power line is down, draped across my driveway. Spent all day clearing driveway so we can now get out. Operating on cell phone charging in car.

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I guess it could have been much worse- glad you survived.Hope you get power back soon.
“Operating on cell phone in car”- Amazing!

Bon courage Kirbert.
Saw some photos, poor Panama…

A big lightning storm last month, the first of them hit our house, fried everything electric.
The second hit one of our trees, fried everything electric in the pool
The third hit a power line, fried everything electric in the whole area…
Two days no power and a month with no phone and no internet…
Cell phone charging in car was indeed the solution!
Makes you remember how life was before the advent of all these gadgets!

May Zeus be with us.

Kirbert"

Sure am glad you and yours are OK. the other stuff can and will be fixed!! Do you have a generator to get you by til the posts and wires are back ?

Amazing that the cell tower survived and you have contact.

Aristides: One local weather guy says that Michael’s remnants are on the way to France and Germany. But as a rains storm, not a historical hurricane!!!

Tis been a tough weather year, fires in the west.
Storms east.

The best to all involved.

Makes my task or preparing my Tax return seem miniscule .

Carl

Carl

Well, thanks to the Forum, the mailman stopped by with a delivery a short time ago.After a search, I just had to get this little gadget!
As a “British” car owner, and also a “British Car” owner, I had no choice. Besides, as my wife has some sort of account with Amazon, it was “free”! Well, almost.


Now I can keep an eye on my alternator, and A/C performance next summer!

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Dave,

Great minds think alike, but differently. :wink:

This arrived in today’s mail for me. In addition to two USB ports and a digital LED voltmeter display it also shows temperature and has what I believe is an ammeter, but I will have to play with that a little more.

Many thanks to Aristides about this gadget. I couldn’t think of a single reason why I shouldn’t have one and wondered why I didn’t already own one.

Paul

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