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Discussion Starter · #1 ·
Hi dudes, hope everyone had a groovy crimbo.

I've been working the whole period and driving the bug most days. I've had 2 flat batteries this week :( and not sure if it's my battery or alternator. Was hoping somebody could look at the tests I've done and tell me what the issue is and/or if I should be doing other tests. Cheers folks, much appreciated.

Dashboard lights
Engine off = All lights OFF
Key first turn = Gen Light ON, Oil Pressure light On
Engine On = Gen Light OFF (after dabbing throttle) Oil Pressure light OFF
When driving with headlights on the gen light ON (faintly) becoming brighter when coming off throttle (high to low revs) or braking. Also pulsates when indicators on

Alternator Tests
Engine running, measured voltage between alternator case and the B+ stud = 10.7 (increased to around 12 after a short time)

Measured voltage directly across the battery posts = 10.7 (increased to around 12 after a short time)

Measured voltage between the engine case and the alternator case = 0

Measured voltage between body sheet metal and engine case = 0

Measured voltage between alternator B+ stud and the battery Pos (+) post. Engine still running as before = 0.17

Disconnected d+ green wire off the alternator and the warning light went out.
Disconnected the wire on the D+ spade and connected a small 12V bulb from the B+ stud to the D+ spade. Bulb on when battery connected. Started the engine, bulb out.

Engine idling: reading at battery and alternator 11.8-12.4
Engine high idle: reading at battery and alternator max 12.7

Battery Drain test

Positive cable removed from battery and VOM meter connected between positive battery and positive cable = DC Volts initially 10.7 and DC milliamps = 1
 

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You should be measuring around 14V at the alternator with the engine at idle unless the battery is completely flat, which it wouldn't be if you just started the engine. I have never seen an alternator fail, only the regulator, so I would suspect this. If the alternator or stand have been painted, make sure there is a good earth path between the two.
 

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Discussion Starter · #3 ·
Thanks for the post, have checked the earth and looks good, cheers.

I put the battery through a repair cycle and charge and then rechecked alternator output and it was putting out 14v but still get the faint gen light when the headlights come on?
 

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The warning light is controlled by the Regulator. If you get 14 V from the Alternator, then the Regulator is suspect, but it may still just be a bad earth, even if it looks OK.
A good connection is needed between the Alternator body and the car chassis, and they are quite some distance apart, (electrically), the current needs to pass through many components, to get to the chassis, and bad connections can be anywhere in that route.
Before condemning the Regulator, run an Earth wire from the Alternator casing to a good clean connection on the car chassis or even directly to the battery earth clamp.
If your regulator is under the rear seat, check it's connection to the car bodywork, (the regulator also needs a good earth).
If earthing fixes the warning light issue, you know what to do, if not, you may need a new regulator.
 

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It may also be worthwhile checking the state of the brushes in the alternator. The voltage can show as OK but doesn't always mean there's much current flowing. You'd be amazed the low quality carbon brushes you can get these days that are very low density and hence wear very quickly and unless an original VW alternator then the chinese ones are definitely worth making sure all is well.

Otherwise as Ben says check the earthing first and then move on to the regulator.
 

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Discussion Starter · #7 · (Edited)
Thank you dudes, I’ll follow your advice and report back. Cheers

can I just clarify about the earthing in the alternator. I thought it earthed through the case and strap/clamp onto the stand (so made sure it was tight and clean). How do you wire an earth to the alternator, I have 1 wire on the B+ and one on the D+ but that’s it, I think I’m missing/not understanding the earthing side of the system (and therefore not sure how to follow your great advice).

can somebody walk me through an earth test and the correct wiring circuit for an alternator with internal generator please 🙏

thanks groovers
 

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Thank you dudes, I’ll follow your advice and report back. Cheers

can I just clarify about the earthing in the alternator. I thought it earthed through the case and strap/clamp onto the stand (so made sure it was tight and clean). How do you wire an earth to the alternator, I have 1 wire on the B+ and one on the D+ but that’s it, I think I’m missing/not understanding the earthing side of the system (and therefore not sure how to follow your great advice).

can somebody walk me through an earth test and the correct wiring circuit for an alternator with internal generator please 🙏

thanks groovers
The Alternator is indeed usually Earthed through it's casing, stand and strap to the engine, but that may not be a 'good' Earth.
To directly Earth the Alternator, (and internal Regulator), run a temporary wire from the Alternator Casing to a good earth point on the chassis, or direct to the Battery Negative terminal.
There is a single screw holding the Regulator cover plate to the Alternator casing, that is a good place to connect the temporary Earth wire via a ring terminal.
Earlier Alternators and DC Generators had a M4 tapped hole in the casing, at the top close to the fan backplate, for a factory fitted Earth wire.
 

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Discussion Starter · #9 ·
The Alternator is indeed usually Earthed through it's casing, stand and strap to the engine, but that may not be a 'good' Earth.
To directly Earth the Alternator, (and internal Regulator), run a temporary wire from the Alternator Casing to a good earth point on the chassis, or direct to the Battery Negative terminal.
There is a single screw holding the Regulator cover plate to the Alternator casing, that is a good place to connect the temporary Earth wire via a ring terminal.
Earlier Alternators and DC Generators had a M4 tapped hole in the casing, at the top close to the fan backplate, for a factory fitted Earth wire.
Thanks Ben, much appreciated.
 

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Discussion Starter · #10 ·
Howdy Strangers, sorry for dropping off... caught the "rona' and been in isolation/headache land for the past 10 days :(

So on leaving isolation and having not driven the bug (but last thing I had done was repair and recharge the battery) it was of course, flat. Battery reading 4.5v! I have had the battery dropped tested and it passed and having recharged it I think it's alright (holding 12.8).

So my question to you good folk is: Is it simply a parasitic drain causing my issues? The alternator seems to be putting out 14V.

Can somebody walk me through the problem-solving. When I disconnect positive cable from battery and measure between them should I get a reading at all (what do I set the volt meter too?).

Would a bad earth on the light switch cause the gen light to glow when it's turned on (only time I see light)?

Is an intermittent stereo loss of power a big clue to cause of issues?

Thanks dudes,
 

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If you charge the battery to 12.8v then leave it disconnected for 24hrs and it’s still in that ballpark then it’s probably okay. Typically the charge will drop to under 12.5v overnight if the battery is poorly.

If the battery was completely drained but otherwise good, connected to the car for 10days, then you have a nasty parasitic drain.
 

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Would a bad earth on the light switch cause the gen light to glow when it's turned on (only time I see light)?
Is an intermittent stereo loss of power a big clue to cause of issues?
Sounds like you have some minor wiring issues, which may not be helping the charging situation.
Bad earth on light switch shouldn't cause the generator warning light to glow, but if the generator warning lamp glows when you switch the lights on, that indicates that the lights are drawing more current than the Alternator can replace, and this will drain the battery.
Are all the lights 'stock', or do you have high power rally lamps or additional lights ?
Ether way, check all the lights and their fuses, all connections should be squeaky clean, dirty connections can cause all kinds of problems, especially in the lighting circuit.
Intermittent stereo power loss indicates a loose connection or a wiring fault which could also be draining the battery.
Is the 'stereo' a little dash mounted radio, or a power guzzling monster amp system ?
Eliminate the stereo from your investigations by disconnecting it completely, make any loose wires 'safe', and just run the car without tunes for a few days.
 

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Discussion Starter · #13 ·
Thanks guys. I’ve removed the stero completely (it’s just a standard mechless head unit) and I’ll test the battery again tomorrow before refitting it. The headlights are upgraded bulbs but that’s all. I’ll try and clean up all the contacts and report back.

thanks for all the help, much appreciated
 

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Hmm, I think first you need to figure out what is draining the battery and then second the charging system needs checking over to ensure it's able to keep up with the demands of whatever you have wired in.
Most multimeters have a current reading ability but this can only handle 10amps but for a parasitic drain that should be enough to find the culprit. A good multimeter will use a 10amp glass fuse to protect the meter from damage.
Then for the genny I'd use Speedy Jims page, if it's still up and running. Otherwise you'll have to research how to do these tests. I don't know if you've checked the genny brushes but this can be a big factor in current flow.
 

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Discussion Starter · #15 ·
Hey good people,

So, I removed the stereo and its wiring and I cleaned up all the terminals and earths as best I could. I also changed out my aftermarket car horn (with relay and direct 12v wiring) and went back to standard horn configuration. I tightened up the alternator clamp as well. The battery was charged and left out of the car for 4 days and dropped from 12.70 to 12.55 after this time (and it was tested at Eurocarparts as it's still under warranty and passed).

I also started to suspect my multimeter was maybe faulty, so switched it for another one and got more normal readings, verified by a third multimeter!

So battery is showing: around 12.8. When car is started and rev'd it shows 14.0 and with headlights on shows about 13.6. So, I'm thinking maybe things are ok now???

I also tried to do a parasitic drain test, but not totally confident I set the multimeter correctly, can somebody check my testing please.

I removed the neg strap from the battery and then tested between the battery neg and the earth strap and got a reading of 0. So, either I have done a duff test or I have eliminated the drain, what say you good folk?

The proof will be over the next week I guess, I have hooked up the battery now and praying it starts in the morning for work!

My multimeter setting and instruction manual:

Tool Yellow Measuring instrument Communication Device Temperature




Font Number Document Parallel Screenshot
 

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Readings look decent with engine running etc.
As for parasitic drain, you've started right, in the highest range (10A) - but you may have a lower ampage drain that would not read on the highest scale (less than 200mA), so step down the ammeter ranges one by one - 200mA, 20mA, 2000uA until you get a steady reading. If you get to the lowest range and don't have any reading then you don't have any drain.
When attempting to measure current, always start on the highest scale then step lower, otherwise you may blow the meter or trip it's protection circuit.

Bear in mind that some modern equipment - ICE gear usually, will take a very tiny current all the time to hold the internal station and settings memory, but this is normal.

Dave.
 

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Redo the current drain as per Dave above.

Your horn relay shouldn't cause any issue unless there was a small voltage running thru the relays solenoid, which would be microamps and would show on the parasitic drain test but the 12V that powers the horn won't matter unless the relay has a carbon track allowing a small parasitic drain too but otherwise it's just a breaker that only passes current when the relays solenoid is energised.
 

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I had an interesting experience with aftermarket horns on a 66 Beetle, the relay operated to connect and disconnect the power to the horns, but a small current was still flowing through the low amperage side of the relay, after releasing the horn button. Tests on the horn button and the relay showed no faults, but we eventually discovered the steering column wasn't fully insulated, so releasing the horn button did not make a 'clean' circuit break. This only showed-up after extensive multimeter tests, it was caused by a new genuine VW rubber steering coupling disc, which was actually slightly conductive, (the later versions of the rubber coupling have steel reinforcement inside). Swapping back to an old solid rubber coupling fixed it, but by then we'd been head-scratching for hours.
 

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Discussion Starter · #19 ·
Update: So left the bug on the drive all week and 5 days later it started first time :) So I'm thinking no parasitic drain, so either cleaning up my contacts/earths, removing stereo/re-wiring car horn has resolved the issue.

I'd like to put the stereo back in now but was hoping for some further guidance please to ensure I don't cause any issues (drain). Thank you sparky heroes.

1. Is there a way of testing stereo head units for faults
2. How would folk wire the following stereo into the car.

This is the stereo I have: Kenwood KMM-BT505DAB

Rectangle Font Parallel Slope Number

  • The unit can only be used with a 12 V DC power supply, negative ground.
  • Disconnect the battery’s negative terminal before wiring and mounting.
  • Do not connect Battery wire (yellow) and Ignition wire (red) to the car
    chassis or Ground wire (black) to prevent a short circuit.
My wiring is as per this diagram:

Rectangle Schematic Font Line Parallel
 

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So the stereos yellow wire goes to a permenant live fuse either a) in the fusebox that not only can handle the current draw of the stereo but also collectively anything else fused by that fuse or B) a fused wire of correct gauge all the way back to the battery.
The red is from the fused side of either the black/yellow accessory position or the fused side of the black ignition live wire both from the ignition switch.

Putting a voltmeter into amp mode with the stereo turned off and ignition off will let you know if the stereo is faulty as when off it should only draw a few mA for the station memory and clock.
 
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