I posted the other day about some electrical issues I was having involving a dead battery, in which I didn't believe the battery was actually the source of the problem. It seems I was right, but that isn't helping me much now, lol.

After a full charge the 'dead' battery was looking good, yet overnight the voltage collapsed to 4.3V and pretty much flatlined at that level. I had a spare battery in the shed that was in good nick, so I put that on the charger for about 7 hours to make sure it was up for the job and let it sit for a couple of days to monitor it first - nice and steady on 12.7V.

Tonight I went to swap them over, and both batteries were still steady. I pulled out the 'dead' battery and put it aside and then put in the 'new' battery and checked the voltage - down to 12.3V just by hooking it up. I then went over to the 'dead' battery and checked it again - up to 8.6V after only 5 minutes disconnected, and nothing being done. I went and did a few things and came back 10 minutes later, and the 'new' battery had dropped a little more, and the 'dead' battery was now up to 8.96V. Just checked it again, and they've changed again - 12.2V and 9.01V.

I'm no auto-electrician, but that strikes me as being just a little bit on the odd side. It seems that something somewhere in the system is drawing a load and pulling the battery down, but how to work out what/where? Can a dud alternator kill a battery even when everything is switched off, or is it more likely to be something else? Whatever the problem, it came on pretty quickly, as there was not even a hint of a problem prior to Friday.

Okay, found a helpful site that told me how to test for parasitic drain, and made some interesting discoveries but am no closer to a solution.

The diode test passed with flying colours, which would tend to discount alternator issues. However, when I tested for current it was reading between 3-4.5A and fluctuating. I proceeded to pull pretty nearly every one of the fuses under the dash for no noticeable effect, and then started on the main fusebox in the engine bay. Pulling the fusible links made no difference, but pulling the one indicated as "40A Lamp" dropped the current back to about 0.6A - pulling others didn't seem to make a whole lot of difference beyond that.

So is whatever is on that circuit the culprit? And if so, what is on that circuit and how do I work out what the problem actually is? I'll keep digging and testing and trying to work it out, but if any decent suggestions on where to go from here would be much appreciated.

EDIT: if I'm reading the wiring diagram properly, the 40A fuse in question is for the alternator? If so, what problem does this indicate given the diodes seem to be fine?

Is the battery putting out 3-4.5A with everything turned off? Unusual to do this without having anything to show for it, like a globe burning (40 odd watts is being wasted) or blowing a fuse (from a short circuit)! You could hook everything up as normal, then feel all your lights for warmth (headlights from inside the engine compartment), or look for a slight glow in multiple lights in the dark. Pull the plugs off the back of the headlight globes and check for current flow. Could be a defective headlight relay. Is the alternator getting warm by itself, with the engine off?
Brake lights that stay on or a boot light staying on will give you the same overnight flat battery symptoms. Keep checking and good luck!

Okay, found a helpful site that told me how to test for parasitic drain, and made some interesting discoveries but am no closer to a solution.

The diode test passed with flying colours, which would tend to discount alternator issues. However, when I tested for current it was reading between 3-4.5A and fluctuating. I proceeded to pull pretty nearly every one of the fuses under the dash for no noticeable effect, and then started on the main fusebox in the engine bay. Pulling the fusible links made no difference, but pulling the one indicated as "40A Lamp" dropped the current back to about 0.6A - pulling others didn't seem to make a whole lot of difference beyond that.

So is whatever is on that circuit the culprit? And if so, what is on that circuit and how do I work out what the problem actually is? I'll keep digging and testing and trying to work it out, but if any decent suggestions on where to go from here would be much appreciated.

EDIT: if I'm reading the wiring diagram properly, the 40A fuse in question is for the alternator? If so, what problem does this indicate given the diodes seem to be fine?

try pulling off the reg plug while checking for a load aswell to see if it drops,these can sometimes create a draw if wired incorrectly/ faulty,and will pinpoint the alt if its the culprit,but like you have stated,faulty diodes that go to ground will cause a draw,but most goi open circuit!,odd

+1 for the problem being with the alternator or regulator. It should be getting quite warm, all by itself! Diodes can show fine with a multimeter that uses a low voltage internal battery, but "leak" under 12V.

BINGO!!!:facejump::facejump::facejump:

The temperature test was the one thing I hadn't tried yet...touched the back of the alternator and I reckon you could just about cook an egg on it - and the last time the car ran was Sunday.

So...can the regulator be replaced on its own, and if so how big a deal is it? Just a matter of loosing the belt, popping the alternator out, screw off and screw on and reinstall?

BINGO!!!:facejump::facejump::facejump:

The temperature test was the one thing I hadn't tried yet...touched the back of the alternator and I reckon you could just about cook an egg on it - and the last time the car ran was Sunday.

So...can the regulator be replaced on its own, and if so how big a deal is it? Just a matter of loosing the belt, popping the alternator out, screw off and screw on and reinstall?

Madmax is on the ball ladies and gentleman!

Id be putting on a new or recoed alternator to be honest,the rectifier plate will be the cause of the heat etc,which inturn could have buggered the stator,reg etc

+1 for reco alternator - usually if the diode pack fails it destroys the reg and vice versa. Magna alternators are either ok or totally rooted. Only a sparky with the right equipment can test stator, diodes and reg. I paid $150 for a recon alternator with 1 year warranty. 6 months into the warranty period it went ape**** - thats how I know about the "feel for a warm spot" trick.

It's a good trick to know, a good one to remember. Thanks for sharing it.

I'll see if I can track down a reco'd one first, that'll be a LOT less painful than forking out for a brand new one. Ouch!

Thanks to all who contributed, much appreciated.

While we are discussing electrical problems, I found my battery light comes on at REALLY high RPM, like 5,000? just flickers?

While we are discussing electrical problems, I found my battery light comes on at REALLY high RPM, like 5,000? just flickers?

Maybe because your car is turboed the revs rise alot quicker and thus causes the alternator to send a massive spike in voltage to the battery and the system reads this as a fault with the charging system?
Only a guess as i have no idea what im talking about:P

hahah.... i like ur theory

hahah.... i like ur theory

What do you mean theory? I base this all on fact, i hope someone comes on now and agrees with me:facejump:

Sorry Wombat, I do not agree, your Regulator will hold this current spike back.

In so far as getting the light at higher revs it may be an issue with the brushes and the armature in your alt being worn and the brushes are losing contact due to jumping etc. Used to have this with the rotary's sometimes with older second hadn altinators.