I just had the "battery warning light" on, about 1000 miles after I changed my previous alt.
Still have to measure it, but it's probably dead again.

Looking for a root cause now, as I don't believe in coincidence.
When checking all ground points, am I correct in understanding that the alt is only grounded through the mounting bolt, and not by means of a dedicated ground strap? Would this not be an improvement?


Any other ideas what could cause this?
Battery is not optimal, however it's used in my daily driver, so I'm sure it works.
I checked the brushes, they look OK however I'll clean them up with some sandpaper.
Diodes only gave an indication in one way, checked between the four red arrows and the stud for the positive connection (see below).

 

While you have it out it can be spin tested on a machine at the auto parts store as it's not practical to do at home on your bench . That way you will know as a stand alone item that the alternator is good or bad ,

On the X300 it takes power to make power so there is a fuse for voltage regular excitation but is shared by many other things , Check if the fuse is blown .


Check with a 13 mm socket and a short extension the main power cable at the upper terminal of the starter solenoid as it ties into the rest of the battery power leads and the large terminal post as it ties through the firewall behind the lower right side of the engine . It's just fwd of the actual firewall .

The Voltage Regulator is a IN435 but they keep sending me a IN221 and doesn;t work .

Your second Alt voltage regulator could be failing as it;s warmed up and heavy electrical load that my not be seen on a auto parts store spin up machine .

Remove one of the noise suppressor leads as there is a possibility of the capacitor shorting inside 44,000 mF if I remember .

The actual ground for the alternator is the case to the engine block and the engine block to car ground is the 15 mm bottom mount bolt of the starter to the car frame . Best from the bollom side with a 10 mm

 

Thx for the detailed reply. Will keep you updated.

EDIT: the voltage indicator on the dash doesn't work (stays on zero all the time). I can't find it in the electrical diagram manual, could you also point me to it, or tell me where the (+)ve comes from? Will be looking at bad connections in the easiest place first, before dismounting the fascia panel...

When having alt problems, it is handy to have a voltage indication on the dash... It wasn't a priority before, however now situation has changed :-)

 

http://www.jagrepair.com/images/Auto.../jagxj1996.pdf

See page 129 on the left side Slate ./ White wire . Hard to see the colors sometimes .

Notice the 3 power sources at the top .

 

Thanks again.
I'll send up 12v through that wire, and see if the voltmeter shows anything... It might not have shown anything because the alt was bad from the beginning (?).

Aghhh

 

They are commonly bad out of stock and best to have it spin tested before installing it . But then a spin test doesn't always show you everything as a real world running / heat and full load .

 

Will do, I have it easy in this case, as I've got one runner (well, not so right now but you've got the idea) and 3 identical cars from OK to really rough shape for parts.
Will try to end up with two runners, but I'll focus on only one right now.

 

Edit: I'll ask this tomorrow again, I just saw that I was asking things without thinking...

 

The alternator needs an ignition switch 12V signal to "power on", but doesn't it need a reference voltage signal so that the voltage regulator knows what it needs to do?
The "dummy" connector port is commonly an "S" port, which is a reference voltage input signal.


I hope to have my first alt load tested today, I'll keep you updated...

 

The IG: ignition input signal is not a fixed reference value , but is the B+ value of the battery voltage with the engine not running which is as much as 12,77 volts on a fully charged battery to as mush as 14.5 volts as the alternator is putting out in a running mode . The typical voltage will be close to 13.5 volts . All the fixing is inside the regulator .

 

Lady Penelope,

just had some time to do a bit more testing.

I asked above which wire sends a signal to the voltmeter on the dash. I understood from your reply it is the slate white wire? This is the wire with name/reference "L". I think this wire only serves to activate the charge warning light (or battery warning light) on the dash (by grounding the wire when the voltage regulator gives a fault).

In the electrical service manual, I only see "charge indicator" (= volt meter?), however could it be that this wire serves both purposes (volt meter and charge warning light)?

I've got 12V at the IG pin on the connector, however when I put 12V on the other pin (L), the voltmeter doesn't move...

 

 

The L wire whats to see something above 12.77 volts of a fully charged battery , so now we have to consider if you have just a indication problem ot a real problem .

Did you see the somewhere around 13.5 on thel arge B + post on the alternator ?

Do you see same time you see the l light at th

My apologies for not timely editing this in time for I only got 4 hours of sleep that night . BE BACK LATER

 

With this alt (case from before, however with another (not new) diode pack, voltage regulator and brushes, I have again 14.5V at B+.
This stays at 14.5V wih headlights on, ... but doesn't rise when I rev the engine.
But perhaps it doesn't need to rise, as the battery has been fully charged on an external charger (? but for this, I'd expect a voltage sensing input at the alt which is not there).

The battery warning light does not illuminate now, however the voltmeter still doesn't move. I'll check for bad connections before doing anything else, however I am not looking forward to removing the dash... Hoping I'll find something under the bonnet.

EDIT: I've given my first alt to a test/rebuild center. This way I'll be sure to have a working spare on my shelves...

 

90% of alternator faults will be caused by voltage regulator, brushes and/or rectifier. You can get a full kit for ~55GBP in UK and its a 15 minutes job to swap all three. You should be able to test voltage regulator and rectifier easily too.
For parts these guys seem to have everything: https://www.jcrsupplies.co.uk/produc..._REBUILD_PARTS
A lot of parts on ebay too.
You can bench test an alternator with a drill, you'd also need to connect a bulb to it, to 'excite' it so it starts.
All these parts below and for more info and more pics have a look here:

https://www.xj40.com/viewtopic.php?f...98219&start=20

 

I tested the diode kit, however I have no idea how to test the voltage reg.
A quick google didn't came up with anything useable, if you happen to know the procedure or a website where it is expained in detail, please do share!

I agree that the motor itself (the house with the windings) is not prone to default, so I changed bearings, turned the sliprings, and changed for (hopefully) good diode kit, brushes and voltage reg.
For the time being, it works.


EDIT: after looking on youtube as well, it appears that the voltage regulator is not a PID reg as I thought, but only an ON/OFF switch. Just need an adjustable power supply now to test...