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Old 05-15-2009, 03:34 PM   #1
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Battery Polarity Problems

I did something monumentally stupid today. I know it was stupid, so I'm not even going to pretend that "a friend of mine" did it!

I replaced all the discs and pads on my car today, and was listening to the stereo for about an hour during the process. After just one hour, my 2004 986 wouldn't start, so I bump started it, took it for a twenty minute drive, then hooked it up to a battery charger. The engine would hardly crank after another hour on the charger, so I decided that I needed a new battery.

132 later and I'm about to fit the new one. Only thing is that the new battery has the vent on the different side as the original one. So, without thinking, just popped it in so that the vent would connect up, and proceeded to connect the terminals. This is where it's riduculous as I'm pretty good with electronics! I put the negative on the positive, then connected the positive to the negative in that order.

The alarm sounded (with such an awful tone that it actually made me lose my balance, which was probably the intention), and there was some smoke and an acrid smell in the cabin. I realised about 10 seconds later what had happened and rectified the problem. However, I now have some serious problems, and they're probably not going to be cheap!

I've looked around on the forums and nobody else seems to have been this stupid, so hopefully documenting this will help any others who want to join the idiot club.

The first problem is that the battery light comes on a few seconds after starting the car. To me this suggests that I've fried the alternator. However, there are quite a few posts saying that it could be the voltage regulator? Anyone got any ideas?

I've also fried the car radio. It's a Becker CDR-23, and it blew the fuse in the fuse box. Replacing it hasn't resolved the problem, so I might think about looking for some sort of anti-surge fuse inside the unit. Anyone know of anywhere else to look?

So I've checked every single fuse in the car - both the normal fuse box, and the current distributor behind the passenger dashboard (I pulled out each fuse and tested independantly, and they're all fine).

Any ideas chaps?



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Old 05-15-2009, 04:18 PM   #2
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The voltage regulator is in the alternator, it is a series of diodes and they are probably fried. On this side of the pond there is a fairly good industry of auto electric rebuilders in most major locations and these can rebuild the alternator at competitive prices vs a rebuild. The advantage is that the rebuild is individual instead of assembly line in a large rebuild factory. Both options are less expensive than buying new.

The radio does have an internal fuse and it's likely this will need attention.

In addition to the fuses, there are relays which should be for the most part unphased unless their appliance was turned on. There are also a series of what Porsche calls Current distributor links, essentially fusible links, which connect certain circuits directly to the battery. On US market cars, this current distribution block is located in the right side footwell. The positive battery cable connects to it on the 'frunk' side making it easy to locate. There are 7 of these fusible links and I suspect some of these blew and caused the smell you experienced. So far as I know, these will only be available from the dealership. On the '04, there are 2 links for PSM, 3 for the OBC (On board computer), one for the ignition lock and one for the engine electronics - some or all of these may have been affected. These can be individually checked with a DMM (digital multi-meter) using the continuity function.

FYI, most vented batteries have a plug on one side which can be pulled and swapped with the open vent hole on the other side to allow installing the battery in either orientation. You simply pull the tube off, remove the plug from the other side and swap them.

Good Luck!

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Old 05-16-2009, 08:24 AM   #3
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Awesome, thanks for the pointers!

I had the current distributor out (that was a job and a half), and checked all of the fuses independently. They were all fine, but it was still good to know that there potentially wasn't still a blown fuse in there affecting something else that I don't know about yet.

I then moved onto the stereo - found the 10A fuse in the back which was blown and replaced that. The stereo then came back on, but it wouldn't talk to the Bose amplifier or the CD player, so I moved onto troubleshooting those.

There isn't an anti-surge fuse in the amplifier - I opened it up and checked - and the red light from the fibre optic socket on the amplifier was present, so it was getting power and probably working ok (given that the fuse in the normal fuse box blew to protect it). I wasn't getting anything for the CD4 changer though, so that then came apart and the hunt for the potential fuse was on. It's not in the main housing - it's under a small cover on the back of the unit, where all of the cables go in (just a single crosshead screw holds it on). This was blown, so I replaced it.

That done, I connected everything back up and off it went! All parts working as they were supposed to! Result on that part!

Now I'm onto what I hope is the last thing that needs to be fixed - the alternator. This is going to be a bastard of a job, I can tell. I'm into the engine compartment and I've loosened off the serpentine belt, and I'm now struggling to get the damn thing out to replace the voltage regulator. I've found a company in the UK that can supply the exact part that people on the forums said I'll need, but I really want to get the alternator out and check it first...


If anyone has any bright ideas, shout!
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Old 05-17-2009, 05:07 AM   #4
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Year and mileage on your Box? Would now be a good time to replace the serp belt while you're in there?
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Old 05-17-2009, 02:18 PM   #5
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Further Update

Hey Husker,

It's a 2004 with 54,000 miles on the clock, so I guess it's due a replacement. I'll get a new one and fit it once the alternator is back in.

Regarding the alternator, it's more than just the voltage regulator. Having looked at it closely, I've melted the coil wires that feed up to the rectifier. I sniffed the evidence of melting (aside from the 5-7mm gap in the coil cable) and it was the smell I could smell in the car immediately after the mistake. That was the one thing that I couldn't work out - the awful smell, but managed to get all but the alternator working again.

There are a few places in the UK that will do a reconditioned alternator for 95 as long as you give them your old one, so I think I'll do that...
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Old 05-22-2010, 02:53 PM   #6
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Current distributor - how can I remove it?

Hello, I had problems with the fog light, no power to the relay. Also the low beam, dont know why yet.. so I now traced the curcuit to the current distributor and wanted to check all the fuses there. I loosen up the nuts that hold the current distributor from the battery side, then tried to move the distributor off in the passenger footwell. But then I found the clearence between the current distributor and an air box? Can someone had taken the current distributor off please help me and tell me how you took it off? Thanks.
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Old 05-22-2010, 03:14 PM   #7
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I fried an alternator because it was dark and I didn't look carefully enough when I was hooking up booster cables. I know that "OMG I'm such a fkn idiot!!" feeling all too well. Fortunately it was a Chevy and it only set me back $500 plus the tow.

There should be a support group for the "terminally" challenged.

'99 black 986
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