Hello,

My alternator just started making a whirring noise, but I had no warning light that the battery was not charging. So first I thought that it would be just the bearing going out, but this evening I had to call road assistance because everything electral was failing...

Battery tested 8.20 volts with the engine running. The ABS was showing multiple faults. Radio and climate control turned on and off randomly. Road assistance also said that the alternator was probably the cause. They gave me an extra battery hooked it to the car battery and charged mine enough to get me home. Everything ran fine after that.

Can anyone please explain to me how the battery charging warning light has NOT come on?

 

ELECTRICKERY?

Some alternators charge with the 'light-ON'.
Sounds like the regulator is faulty or wiring between the ALT and Battery.

Check continuity from alt to starter and then starter to POWER STUD on false bulkhead.
MEGA-FUSE in the boot can also fail or have a faulty connection but Starter would be affected.

 

What is the condition of your battery cables, ...you should have no corrosion or you'll have issues keeping the battery charged amongst other electrical issues.
Verify your grounds are good, ...this especially includes the lanyard on the ground cable for the battery, these can go bad and look fine.

I had an issue with mine about 10 yrs ago where I would have a total power failure after shut off. I'd come back to go and had no get in to go.
I followed some of what Bob stated until I came across the faulty lanyard. The MEGA fuse is relatively cheap and easy to replace and can give intermittent issues as Bob notes.

I attached the electrical and troubleshooting guide for review.

 

These cars are usually pretty good about warning you when something is not quite right.
My suggestion would be to use a OBD-2 scanner to confirm your voltages both running
and not. I would certainly inspect the grounding as many issues can result from there.

 

That was actually the first thing I wanted to try. Unfortunately the live data from Voltage is not listed as supported in my OBD2 scanner (I use BlueDriver).

Battery cables are good. Also no corrosion on the MEGA-FUSE behind the spare wheel. Grounds looked good. I clean the contact points of the battery every now and then.

I took the one between the chassis and torque converter housing, just to be sure, removed it, cleaned it at the connectors and put it back.

I still had a used alternator lying around, so I installed that one. It's a bit awkward because you can't actually reach the top bolt, but after a lot of fiddling the old one was out and "the new one" was in.

The battery now charges nicely with a running engine (14.00 - 14.10 volts) instead of the 8 volts on the side of the road (also with the engine running. But then I had turned off everything I could such as the radio, climate control, etc.)

The problem is solved for now, but I still find it strange that the battery light did not come on that night.

 

As the charge light comes straight from the alternator. It is not uncommon charge light to behave like this. Light comes on when the wire is grounded through the alternator. When the alternator spins and it's charges, that ground switches to the voltage. Sometimes alternators do broke that way that there is voltage in that wire all the time and therefore bulb in the dash does not light up. Sometimes light starts to glow. But this depends from the dash how it is designed.

 

I remember on an old '69 SS Chevelle the alternator light would not come on
unless the belt broke or otherwise stopped spinning.

 

...if your grounds, wiring and alternator charge are good, you should never have to clean your terminal points. I've had my Jag for 18 yrs and have never done so...just saying.

 

There is a fuse as it takes power to make power in this instance

# 2 / 5 amp Engine " compartment " fuse box

This fuse can blow for reasons other than the alternator voltage regulator , it is shared by other systems

this fuse powers the voltage regulator for alternator excitation that regulates the alternator output voltage

 

One of the systems is the rain sensing module , remove the connector

The other system is the windsheild washer fluid nozzle heaters that may have got cold enough to have been activated ( temp sensor in the right wheel brake cooling duct at least on the X300 )

The whirling noise can be a front bearing on the alternator going bad ( propper belt tension ? )

I had this on mine ( X300 ) and took it to a alternator shop to replace the bearing as new out of box or rebuilt alternators these days are junk

 

I did not meant I cleaned them every week, just when I needed to disconnect the battery for example to remove the guage cluster (change lightbulbs). I have the tool, the terminals were exposed, so why not clean them quick while I'm at it (was my thought).

 

I had a Vauxhall Carlton years ago that didn't charge but had no warning light, took a while to work out as it'd charge for the first 10mile or so & then fail, so when I got the alt tested it worked.

Turned out to be the diode pack burning out so the car was seeing voltage from the alt, hence no light. But sod all amps so the car wasn't charging.

 

This makes sense. I also had no power steering for a very short time when I took the turn (to stand somewhere safe). I didn't think much of it at the time, because of all the Christmas lights and error messages on the dashboard.

But this would mean that the alternator was indeed using a lot of power and causing the belt to slip.

Thanks