Alternator problems?

Quick question while the car and I cool down, the battery light came on during a short trip, it look fairly dull but after stopping and checking battery connections the light was brighter then got duller idling around to the battery place. He tested it and said it was fine (nearly new) but the light remains on. I can see the alternator but how do you remove it,from the top or bottom?
I take it that the brushes are worn but it is still charging 13.7v on revs. Could there be something else causing this type of fault?
1983 xj6
Col

From the bottom.

It’s a little tricky. You’ll have to disconnect the anti-roll bar and shift it aside to allow enough room for the alternator to drop down.

Sometimes the large oil cooler hose clamped to the front of the subframe needs to be un-clamped and shifted aside a bit as well

Using 1/4" drive sockets may help, given the tight quarters

There’s not much slack in the wires so I disconnect the main output wire from the “+” post on the firewall and remove the several small clamps that hold the wire to the body of the car along the lower part of the engine bay. This allows the wire to come down with the alternator, making it easier to disconnect. Check this wire for corrosion under the insulation.

The black/brown (or is it brown/black?) wire is probably baked, crispy, and fragile. Be care. Check the connector carefully as well.

That’s all I remember at the moment. Been a few years since I did one. Others will chime in with more

Cheers
DD

Thanks Doug, wish you lived near as you have helped so many times and I owe
you a beer or two. Tomorrow is a day out in the MG, fair bit easier to work
on but not anywhere near as comfortable so Thursday is the start of the
fix. Still haven’t fixed the Park (handbrake) but I am hoping to get it
through the annual rego. check at the end of the month. I’ll let the forum
know what happens.
Col.

**
Before removing the alternator, Col - check the black/brown wire that Doug mention…

With ign ‘on’ the wire connects the battery (12V) through the lamp to ground in the stationary alt - the lamp lights. With the alternator turning it produces voltage; with voltage on both sides of the lamp - the lamp light goes out. Ie, with equal voltage on both side of the lamp, there is no light…

The point is that the lamp may shine dimly if there is a voltage difference - very little current is required to light the lamp, so alternator current output is not involved. Principally, the lamp may ‘glow’ both with high batt, low alt voltage - and vice versa…

A sometimes problem is that the brown/black wire disconnects from the alt terminal, making more or less contact with ground. With rather normal 13,7V from the alternator; it is too early to suspect the alt. And it’s easier to test the alt in-car to verify if it is faulty than to take it out prematurely…

Frank
xj6 85 Sov Europe (UK/NZ)
**

Thanks Frank, I will look into the wires first.

Doug is correct out the bottom.
Out the bottom. Funny there’s a post I did a couple months back about this very question. check out the thread it give detail on how I got the alternator out.

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So four hours later I ha e the alternator out but I had to remove both sides of the stabiliser bar to do so. No time to get to the auto electrician today but the bearing feel ok. So off the road for a while to give my knuckles time to heal. I have no idea how to get it back together but time will tell.
Col

Well done !

Four hours ain’t bad at all for a first-timer. :slight_smile:

Cheers
DD

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Just returned from testing the alternator and it looks like the regulator
is shot. Can not procure a new one so new replacement alternator is on it’s
way . Gives me time to clean up the oil leaks that have appeared in the
last 30 odd year that I have never been able to see.

Tried everything I can think of, cleaned the + wires to battery checked the wire to the dashboard, but the light remains on. When warning light wire is connected to earth the warning light is on. That indicated the wire was not broken or even a bad connection?
Don’t know where to go from here. I hate DC as it does things AC doesn’t.
Col

By the way new alternator fitted.

its slightly possible you have either chafed/faulty wiring (that is earthing) when it should not, or your new alternator may be faulty

for the 1st, you could try running another wire instead.

Have you fault found using a multimeter?

(I am only familiar with alternator installations up to S2)

**
Identical symptom with the new alternator fitted, Col - not merely ‘similar’…?

This is why items should be tested before changing - even if the chance that two alternators have the same fault is miniscule, and the fault may not be with the item tested…

Question; was the alternator replaced with an identical one? If not, there may be some differences in the connectors. In any case, with the black/green connected; the lamps should be fully lit both with the wire grounded and when connected correctly to the alternator. And the lamp should of course be ‘off’ when the engine is running…

A faint glow indicates a voltage difference between the battery and the alternator side. The alternator should deliver rated voltage from around 2000 rpms, but with a low/defective battery the alt voltage, read at the battery will be lower…

As an aside; with some alternators the green/black wire is needed as an exciter to ensure fast build-up of the alternator fields - but voltage readings at the battery is an indication whether the alt is charging. The lamp itself is a warning only. I trust the alt belt is properly tightened…?

Frank
xj6 85 Sov Europe (UK/NZ)
**

The is a possibility that the wire is chafed but I can not see where inless
it is under the dashboard. The chances of the old alternator and the new
one both having the same fault are fairly remote. If I could find where it
connects inside the car, looks like pulling tacho out to see, then that
will be my next step. There appears to be no fault with a multi meter but.
Who knows with DC?
The saga continues…
Col

Frank_Andersen https://forums.jag-lovers.com/u/frank_andersen
January 28

Testie2:

Tried everything I can think of, cleaned the + wires to battery checked
the wire to the dashboard, but the light remains on. When warning light
wire is connected to earth the warning light is on. That indicated the wire
was not broken or even a bad connection?

We yes, although the original problem was that the light came on dimly and
increased as revs increase. The problem remains almost the same although
the lamp does not seem to be as bright on revs. No the alternators were
different but the supplier assured me that they were compatible. There are
only two connections that are used on the new one,although there are many
more ,plug, spades etc. The two brown wires that were and are still
connected to a single + and back via the stud on the bulkhead to + battery.
The other wire comes from the W+ to the ignition/battery/alternator light.
The belt(brand new) is tight and there is no slippage. The volts at the
battery with the engine off is 12.6v and about 13v at idle, increasing to
14.1v at speed.

That sounds reasonable, Col - though it doesn’t not explain the glowing…

The alternator connections might be checked further - not all connections are directly compatible to the car.s lay-out…

Frank
xj6 85 Sov Europe (UK/NZ)
**

Frank_Andersen https://forums.jag-lovers.com/u/frank_andersen
January 28

Testie2:

The volts at the

battery with the engine off is 12.6v and about 13v at idle, increasing to

14.1v at speed.

If I can get to the actual bulb, remove the wire that runs to the
alternator and run a temporary external one back to the alternator and
things go back to how they should be, then the “fault” must be I the wire
that runs around the engine somewhere. Does that sound feasible? Annual
rego check tomorrow and as the alternator is charging the battery I can
just ignore the light for tomorrow?

That sounds reasonable, Col - though it doesn’t not explain the glowing…

The alternator connections might be checked further - not all connections
are directly compatible to the car.s lay-out…

Frank
xj6 85 Sov Europe (UK/NZ)
**

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January 28
Frank_Andersen Profile - Frank_Andersen - Jag-lovers Forums January 28
Testie2: Tried everything I can think of, cleaned the + wires to battery
checked the wire to the dashboard, but the light remains on. When warning
light wire is connected to earth the warning light is on. That indicated t…

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Test No1: If you disconnect the alternator light wire at the alt, and apply 12V, does that extinguish the light?

Now there is a good question! I’ll try that tomorrow.

Col:

A master of electrickery in Ac or Dc, I am surely not. But, I do claim to be a more than decent analyst, based on experience in my former profession.

One of your past posts indicated that the new alternator has more spades than the original and that only two are needed, I suspect you have on properly connected. The large post back to the post on the firewall. Fairly clear as your meter readings show the alternator is making volts and the battery is receiving them.

So, that raises two questions?

  1. Is the warning light connected to the “correct” spade?

  2. How to test the warning light circuitry in the car ?

As for 1. Did the device come with installation instructions? If, so, did you follow them? If not, identify the maker and call their tech support folks for help.

As for 2. Substitution. A test lamp. Disconnect the car’s wire from the warning light spade on the alternator. connect the lamp’s + leg to the spade on the alternator. Connect the lamp’s - leg to ground/earth,

Fire up the engine, Does the test lamp have the same issue? Or does it light with the engine off and extinguish when running.

On doing these, I think you can draw conclusions. And get things right.

Carl

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