Battery/Alternator Warning - Investigation ongoing

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Hi all-

I asked about battery cable removal a while ago to start solving this problem. There weren't may replies, but it gave me some time to research and see what all might be going on, and what I might need to investigate.

Here's what I get, every time I start the car:
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As it turns out, removing the positive battery cable is very easy on a Cayman. On the passenger side, in the frunk, at the cowl, take off the plastic panels so that you have good access to the area to the side of the battery. You may find a lot of gross things down there. What you're looking for, however, resides on the firewall, and you can follow the positive battery cable to it. What you'll see is a quick connect: a black housing with a red locking slider. I used a flat head screwdriver to move the red, locking bit down and then you can wiggle the connector off a long, unthreaded post. There may, or may not, be corrosion present which may, or may not, be causing weird issues with your car. I did not take great (read: any) pictures of this part of the process, as there are good DIYs out there with good pictures on 997 forums.

There are 2 13 mm nuts that hold the power distribution box on the inside of the car; remove those then head into the passenger footwell and get ready for some fun. Some things I did to make things easier to remove the box and bring it down into the footwell:
- Remove any trim on the left side of the footwell that might interfere with pulling the carpet back, which you're going to want to do. Our car has a Bose system, and the subwoofer is down there. You get it out of the way by removing a small vent thing (one Torx screw, and then it unclips pretty easily), followed by the removal of a larger Torx screw. You push the subwoofer assembly toward the rear of the car and then you can get it away from the central tunnel. There's a single connector that can be undone and the sub is totally free.
- Remove the foam thing that is under the glove compartment. Mine was held on with 4 plastic screws that I was able to undo with my fingers, no tools necessary.
- I didn't do it on removal, but should have: there's a rubber hose held on by an Oetiker clamp to a drain of some sort. Undo that and get it out of the way.

The distribution box is then able to be maneuvered down, though it takes some time and finesse. That, or some muscle and cursing. At any rate, what I think helps is to try to push it toward the center of the car as much as possible and then slide it down.

Once it's down far enough, the box is hinged at the bottom and you can open it, but there will be a green seal that you'll have to break. Once there you can undo a 13mm nut that is the power cable to the distributor or starter. After that, you can remove the post thing from the back of the distributor box via some wiggling; there's an o ring that will make it a snug fit.

That bolt/post thing is what I decided to replace. There's a TSB that indicates that corrosion on that part causes all kinds of issues with the car. It's what I was hoping was causing the generator warning shown above (TLDR: it wasn't and the issue still needs fixing). You can buy a repair kit for a lot of money, or get a 996 distributor box and remove the bolt thing from that (it's an older design, but threaded on both ends, and looks like what the newer repair kits from Porsche do). Being cheap (frugal, cough, frugal), I decided that I would go the path that others have suggested and tap the post. I did a poor job, and compounded it by trying to get fancy and put on an aluminum oxide coating to protect the new threads. It's...not good, and I didn't want to break out my electroplating setup, so I went with plan B.

Here is plan B, with the messed up post in the background:
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Still wanting to be fancy, that is threaded aluminum rod (not as good for conductivity as copper, but better than steel) with an aluminum coupling nut, aluminum nut to lock things down, and a fancy sealing washer to make up for the lack of an o ring.

It didn't work.

The new, fancy washer was just too big to fit down into the cavity where the original bolt/post resides. So, onto plan B.2:
20230915_200504.jpg (6.33 MiB) Viewed 102 times
Here there's a standard stainless steel washer and silicone gasket.

Put that into the distributor box from the rear and snug it down with another aluminum nut. Just to give myself the best chance of success, I went through and used DeOxit and DeOxit Shield on the cable end and mounting flange in the box.
20230915_201405.jpg (4.45 MiB) Viewed 102 times
Maneuver the box back into position on the firewall and snug it down from the frunk area.

Meanwhile at the other end of the batcave, I started making new wires for the battery. For the main battery cable, I used a Fusion lug, where there's a big slug of solder that you put your wire into.
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With a standard terminal on the other side, a new positive cable made from 2 gauge welding cable was complete.
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There's an different red wire that used to attach to the fancy positive battery lug. I changed that up a little so that it attaches directly to the battery distributor post and has a quick disconnect. I don't anticipate doing much quick disconnecting, but if I ever need to make a new wire, I'd rather not have to cut a soldered butt joint in the wiring.
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Here's everything hooked up.
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The connections at the firewall:
20230916_130211.jpg (3.22 MiB) Viewed 102 times
And finally, for now, a hard to distinguish photo of the additional red wire that now goes from the loom to the power distribution bolt.
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On first start up, I got the warning again, so I have definitely not yet fixed what's wrong.

I've replaced the alternator voltage regulator, and checked that, indeed, the voltage at the battery is >14V while the engine is running. However, as this warning comes before I start the engine, I thought that the issue would be found in some of the pre-checks that happen prior to ignition.

Previously, I've looked at the pins on the DME plug but didn't find anything wrong there. I may have to go back and look at those more closely, as that is another fix that I have read reported.

After that, I'm currently at a loss. The car is running on a replacement engine, which came from a manual car. I see that there are different alternators that correspond to auto vs manual cars (I think), so the car has the alternator from a manual car. I don't understand why that would make a difference, however. I have the old alternator and can swap that in, but that job sucks.

Any ideas would be greatly appreciated.



1990 928 GT
1990 928 S4
1991 944 S2
1993 968
2002 911 C2