Volvo 940 not charging

[taiwan740]

Hello

Drove to work this morning to notice the battery light very faintly on at idle. Immediately thought alternator. Went out at lunchtime with multimeter, checked battery voltage at 11.9V (i left the sidelights on which didn't help) with car not running, and 11.3V with car running. So not charging, fair enough. No cables flapping about and the alternator was going round as well. Battery is not old.

So its the alternator, fine, easy.

But is it?

When I turn the key on (not engine) I get only the lambda light, handbrake and oil light (intermittent fault on this one). No battery light at all. Red flag?

My main concern is that the car does have a problem when its been sitting in the rain for days that the speedo, oil light and odometer either don't work for days or go loopy, I assume due to moisture. Could it be that the battery light has gotten damp as well and therefore the alternator isn't activating?

I have a spare instrument cluster in the parts bin but no alternator. Should I just change the alternator and shut the hell up, or is that battery light thing weird?

For those interested, Its a B230F 940 GLE MK1 automatic with about 210,000 miles on it. Had it for two years just this week, saved from scrap.

cheers

[aardvarkash10]

from recent experience, the failure of the alternator CAN lead to a very entertaining light show on the dash.

If you want to check here's what you do.

Disconnect the sense/warning light wire from the back of the alternator - this is the smallest, lightest wire and usually connects to a spade terminal.

With the ignition ON but the engine not running, the alternator light should be OFF.

Use whatever is handy to connect the wire you disconnected to earth. With the ignition on but the engine not running the alternator light should come ON.

If this happens, cool - your warning light circuit is working correctly.

[taiwan740]

Thanks, sounds logical - easiest earth would be the alternator body itself I suppose? If not, I've got some 17A wire somewhere i can hook up.

That's not gonna cause the battery to unleash it's whole current down the wire though is it? My understanding of electrics says no but I have managed to melt and burn jump leads before so I'm no expert.

[aardvarkash10]

Originally Posted by taiwan740

Thanks, sounds logical - easiest earth would be the alternator body itself I suppose? If not, I've got some 17A wire somewhere i can hook up.

Yes, the alternator body is earthed.

Originally Posted by taiwan740

That's not gonna cause the battery to unleash it's whole current down the wire though is it? My understanding of electrics says no but I have managed to melt and burn jump leads before so I'm no expert.

I generally aim to avoid killing cars and owners when recommending a test process. However, this is the internet, advice is cheap, and you are correct to ask!

No, the test will not do any damage whatsoever.

[lnparry]

Hi Taiwan 740,

With everything electrical turned off and engine running at tickover you should be getting 13 to 14V across the battery terminals using a multimeter. With everything possible turned on (lights, fans, wipers, heated rear window / seats & radio plus anything else you can think of you should still get 12V across the battery terminals at tickover. Anything less and you probably have a weak alternator.

I think batteries need to be tested using a drop test. It is no good just getting 12V across the terminals. They need to be put under load to see what they can do. An auto electrician should be able to test this.

I have had batteries die on 740 / 940s previously and the dash display / instruments / wipers all seem to go on a go-slow just before the battery died completely.

Good luck,
LeeP

[Laird Scooby]

Ash beat me to it with the first test, when the battery warning light comes up on the test, it should also bring on the ABS and a couple of other warning lights too.

It sounds suspiciously like you do have an alternator problem but do the test first and report back.

FYI charging voltage at idle with no load should be 14.4V with a cold voltage regulator and 14.0V with a warm regulator.

YOur battery isn't fully charged as it would be 12.6-12.7V after settling for half hour.

Do the test Ash advised and let us know, we can do more tests from there.

[aardvarkash10]

Originally Posted by Laird Scooby

Ash beat me to it with the first test

One of the distinct advantages of living 13 hours in the future.

[taiwan740]

aardvarkash10 - your test didn't work, grounding the battery light cable didn't do anything.

I installed another alternator and it works and charges with the battery cable connected, so we're all good.

My old alternator is the bosch 65A one - where can I get a kit to rebuild this one? and what kit do I need? volvo part number is 3544624

[Laird Scooby]

Originally Posted by taiwan740

aardvarkash10 - your test didn't work, grounding the battery light cable didn't do anything.

I installed another alternator and it works and charges with the battery cable connected, so we're all good.

If earthing out the warning light cable with the igntion on didn't cause the warning light to illuminate, this alternator is not likely to work either!

However, because of the wiring of the instrument cluster, you may have got the other warning lights on self-test (ABS, washer fluid and a couple of others) which would be enough to excite the alternator.

Does the charge warning light come on now when you first switch the ignition to position 2 without starting it?

[taiwan740]

Originally Posted by Laird Scooby

If earthing out the warning light cable with the igntion on didn't cause the warning light to illuminate, this alternator is not likely to work either!

However, because of the wiring of the instrument cluster, you may have got the other warning lights on self-test (ABS, washer fluid and a couple of others) which would be enough to excite the alternator.

Does the charge warning light come on now when you first switch the ignition to position 2 without starting it?

Yup, perhaps the alternator body isn't grounded after all, or I just got a crap ground when I did the test.

When I connect the small red wire, battery light and everything else works fine and it charges. Disconnected, it gets the same symptoms as before with the bad alternator.

I wonder if that ring connector on that cable was just a bit cruddy or something. I will bench test the old alternator somehow or something I guess.