alternator light

jim sky · 07-20-2006, 10:37 AM

I thought the alternator on my n/a 924 had failed, however when tested, it and the voltage regulator were fine. As the battery is dead I connected the battery terminals through jump leads to my VW van. The car started and runs but the ignition warning light doesn't go out although it goes fainter with a few revs applied. The needle on the voltmeter is way over to the right, as far as it can go past the sixteen volts. I'm not keen on replacing the battery yet until I have a clearer idea of the problem. Can any of you fine upstanding members rise to the challenge, thanks for your time.

Razorback1980 · Razorback1980's Garage

Try cleaning all connectors from the alternator to the battery INCLUDING ground wires. Sounds like the alternator is putting out the voltage but it isn't reaching the battery. I would start with battery cables and then move on to the starter solenoid and then check the ground between the battery ground and engine and then firewall making sure that when you put an ohm meter on those items, they ohm out to zero.

jim sky · 07-20-2006, 04:12 PM

oh heck Hank, not that skanky old 924 earthing (grounds) thing again. I cleaned up all the body ones when the fuel system was feckin about, didn't consider the under bonnet (hood) earthing. Thanks for taking time to reply.

JivenJim · 07-21-2006, 11:02 AM

Sounds like bad Battery to me. Diconnect Battery and try Jumping direct to Battery Cable without Batt attached. If warning light goes out then it's the Batt. A Dead Batt will load down a system even under good charging conditions.

morbid · 07-21-2006, 08:05 PM

If the bat is good, check the blue wire from alternator.

onZedge · 07-21-2006, 08:24 PM

NEVER start your car without a battery installed !!

morbid · 07-21-2006, 08:28 PM

Quote:

Originally posted by onZedge
NEVER start your car without a battery installed !!

Yup! That would burn your alternator, DME, or whatever doesn't have a fuse.

onZedge · 07-21-2006, 09:06 PM

Yup! and then some. That is why the voltmeter was pegged. Without a battery installed, the alternator will output unregulated DC voltage with a composite AC voltage waveform as high as 60 VAC.

Just my 0.02 V...

jim sky · 07-24-2006, 02:30 AM

so I guess at one point there I having two alternators whacking charge into the system. I guess the next check woud be to instal the good battery from the van see if that sorts it. Should never give a carpenter a set of spanners. Thanks for sll your input.

Eldorado · 07-24-2006, 02:57 AM

1. jump your car with your battery installed...

2. remove the jumper cables.

3. remove the negative lead from the battery with the car running.

4. if your car dies right away, it's the alt... if not, it's the battery.

Razorback1980 · Razorback1980's Garage

I don't like the idea of removing anything to do with the charging system with the car running. Take the battery out and take it to the auto parts store and have it checked. It's really easy and safe and won't damage your car in any way.

...and remember to remove the negative cable first.

onZedge · 07-24-2006, 07:16 AM

...and reinstall the negative cable last.

jim sky · 07-24-2006, 08:24 AM

When I jump started it and took the jumper leads off the engine died, dead as a nit. Is it really looking as simple as a u/s battery?

jim sky · 07-24-2006, 11:58 AM

I put on the good battery from my van, the engine starts really well. The bloody alternator warning light still doesn't go out, it goes dimmer as the revs are increased but never quite out, also the voltmeter has occasional drops from 16v+ down to 12v if you tap the gauge glass it pops back up to 16. Is a gallon of petrol and a box of matches the wrong answer to this problem?

Eldorado · 07-24-2006, 02:08 PM

well you've checked your battery, now it's time to check your alternator... most places that are able will do it for free for you...

jim sky · 07-24-2006, 02:55 PM

the alternator was off the car and checked last week by a local alternator rebuilder, it was fine, voltage regulator was fine too. Would it not also be possible to cross check by putting a volt meter across the battery terminals with the engine running? I seem to recall a good battery and alternator would read up to 14.5v. Feasible?

Eldorado · 07-24-2006, 03:41 PM

that's right..
worth a shot..

have you cleaned all your grounds?

mlue · 07-24-2006, 07:54 PM

Quote:

Originally posted by jim sky
the alternator was off the car and checked last week by a local alternator rebuilder, it was fine, voltage regulator was fine too. Would it not also be possible to cross check by putting a volt meter across the battery terminals with the engine running? I seem to recall a good battery and alternator would read up to 14.5v. Feasible?

Thats the first check that you should have done, that tells you if the alternator is putting out properly.

What condition are the cables going to the battery and alternator in? If they are coroded they will make a big voltage drop and all your voltage readings will be low and the lights will be dim.

Razorback1980 · Razorback1980's Garage

The alternator furnishes power back to the battery through the starter solenoid. Check to make sure each of those wires are clean and then coat them with dielectric grease. If your alternator checked good and the battery is a known good one, then it's a bad connection somewhere. Could be a ground as well. Use your ohm meter and check the ohms between the alternator case and the battery ground, if you don't get a 0 reading, then start by cleaning the battery ground cable both at the battery and the engine block, then move on to the other grounds until you get a good reading. Then disconnect the positive battery cable and check the ohms between the alternator post and the battery cable end. Again, should be 0 ohms.

jim sky · 08-15-2006, 09:28 AM

got to the end of this one. Took the starter off to check the connections and found that both the cables to the alternotor were perished, the insulation was cracked off the copper wire crumbled. The easy bit was the wiring, put it all back together and it's as right as ninepence. A big thank you to all contributars