I'm completely new to these cars...just got a XJ300 4.0 ...don't really know much about them at all. Car is not charging, last owner put a new alternator on ( but is it new...looks like a reconditioned at best and possibly second hand ) I've checked such earths as I can find still no joy. There's two wire into it other than the main output post...both white wires. I'm asssuming one is an exciter and the other a dash light? ...so presumably one of them should have 12v on it once the ignition is on?

The issue is slightly confused for me by the fact that there is a 'thing' the like of which I've never seen before, right next to the alternator. A black plastic cylinder, wired to the alternator via a red two pin plug....it's wired to the output post and the alternator earth ....what's that then?

 

I went through this already. You might want to check through the threads that I started. Check the 5amp fuse on the right side of the engine compartment. If it is blown, replace it and if it blows again, follow my process on a few threads back.

 

Checked all the fuses ....how do i search for your thread? I'm not great with forums ....can you post a link?

 

Ah ..thread called 'voltage dial goes to zero' ...got it ....I'm pretty sure i checked all fuses but I'll have another look ...i guess the easy way is to see if the washer pumps work!!!!!!

 

The washer pump test would be a fast and easy way to test for the suspect fuse .

You are correct on the function of the 2 wires in the round connector . The suspect fuse # 10 / 5 amp RH engine fuse box is for the voltage regulator excitation .

The voltage you should see on the large terminal post on the good alternator is around 13.5 to 14.5 volts DC which is above the full battery charge of 12.77 volts .


The large cylinder is a alternator noise suppressor .

The fuse diagram can be found in page 18 of this Doc . # 1 fuse is always closest to the box terminal post .

The link Cdma referred to can be found here :

https://www.jaguarforums.com/forum/x...othing-200398/

You can replace just the regulator as part number IN435 and is easy . But the 2 different Ebay venders kept sending me a IN221 .

You can spin test the alternator at the auto parts store for free and would be suggested before you install a alternator off the shelf .

The engine mound hinge bolt goes through 2 outer bushings on the clevis but do not need to come out , just the bolt . The clevis can pinch the alternator and not come out , just use a large screwdriver to lever in out .

 

An alternator noise surpressor.....never heard of such a thing! It's not physically connected to the alternator...how on earth does that work. ? I'm assuming I can leave that disconnected whilst I'm mucking about doing tests?

 

The noise suppressor ( 44000 UF capacitor ) smooths out the AC ripple signal better into a flat DC after it come out of the diode rectifier which does the most AC to DC conversion but not perfectly .

You can leave it in place and you can test the suppressor easily with a meter .

Kept it connected during the whole charging system test and more likely to keep the wiring on the alternator straight .

 

So it's just a bloody great big capacitor! Well, well. That could be the source of a fault couldn't it? If that's gone closed circuit at DC?

 

low percentage chance compared to other things in the charging system . Personalty I would leave it alone for now .

 

The alternator is on the bench....do I need to connect the output post to the excited terminal to spin test it?...if so...which of the three spade terminals is the exciter?....and as long as the surpressor is showing infinite restance at DC I can assume that's not the problem....

If there isn't a fuse blown ( I don't think there is) presumably a lack of supply to the exciter is the likely cause of non charging? ....can I choose that by simply looking for 12v on one of those white wires going into the three way connector (why the hell they are both white baffles me!) ....if it's missing I can jury rig a supply to the appropriate terminal and see if it brings the alternator to life?

Thanks for your help Lady Penelope....great to connect with someobswho knows !

 

The parts store will spin it as is not practical at home to get it up to speed . There is an adapter between the test machine and the round connector that has to be correct .

The White / Blue wire is the power to the regulator . The other Slate / White wire will not have power . The Ignition key will have to be in the on position .

A capacitor test would be climbing resistance as it charges up from the meter . Short the pins to discharge and watch it climb again with the meter .

 

The diagram of the pins...is that looking into the alternator or the plug.?

The plug has only two wires, so 'sense' is n/a ?

The two wire looked the same colour to me...reassuring to know they are actually different... that'll help when I'm next in it....thanks again so much for your help

 

Let me look at mine for pin map

My knowledge is but a island in my ocean of non - knowlege .

 

If you look at the car side connector the White / Blue wire is on the right side of the 2 vertical sockets on the connector face and not the wire side

 

Just ensure that you connect all the wires, I forgot to connect the large feed to the starter.....no charge
On another track the AJ16 engine in your car does not normally suffer from chain tensioner problems, they are very strong engines. My brother had a 3.2 and sold it last year with 340,000 Kim’s on the clock. Only sold to upgrade to a later X308.