Beetle TDI intermittently dies

Symptoms: 2 days ago, I went to start my 01 Beetle TDI Automatic Trans and after the glow plug light went out, everything went completely dead, zero power. I didn’t move the key or push any pedal, it just died. After jumping it, it ran fine and took it to Autozone where they tested the battery and alternator which they said were both good. The battery is about 1 year old. It ran fine after that, until today when after driving about 50 Miles, it died at a stop sign but restarted right away. Then I got home and it died when I parked and again went completely black, no power. It seems like a relay is shorting to ground intermittently, possibly the glow plug or starter relay? Any help is appreciated!

Probably one of the battery terminals is not adequately connected.
On my cars, I need to use a small shim of aluminum license plate (totally clean of covering) because, apparently, the VW connectors are designed for more specific batteries with slightly larger diameter posts.

No matter how hard I tighten them....the connection is not reliable.

I clean and insert a vertical shim approx. 1/4 to 3/8 inch wide and never have a problem again. Works for me!

Check the ground UNDER the battery tray.

If the battery posts are clean and tight, then I would do as suggested above. There are multiple grounds under there that can (always) use a good touching up.

I agree with oilhammer.
If that one is not good anything that grounds to the body is bad.

Thanks for the advice! I checked all the above and the only one that was definitely loose was the negative battery terminal. That said, I also looked under the fuse box on top of the battery and found a mess. This is actually my daughters car which I bought for her a few months back. I found the fuse box had a previous blow which caused the plastic to melt preventing the wires from being secure which caused the large AWG red and black wires to occasionally arc. I secured and insulated and am holding my fingers crossed that this issue is fixed. Now my daughter texted me today and said the brake light is now flashing on her dash....back to the drawing board.

Check the brake fluid level. Idparts sells a new fuse block.

https://www.idparts.com/battery-fuse-box-a4-late-p-3898.html

The flashing Brake light ended up being a simple fix, the ABS fuse in the fuse block was blown. I also found the fuse was not the correct size. All three fuses should be 30A, but I had one 30A, one 20A (this one blew in the ABS slot) and a 10A. I’m realizing I need to comb over this bug to make sure everything is what it should be because whoever previously worked on it didn’t pay much attention to detail...

ojorek said:

I’m realizing I need to comb over this bug to make sure everything is what it should be because whoever previously worked on it didn’t pay much attention to detail...

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Glad your making headway.

If you don't have detailed records did you change the timing belt & related items?

How many miles on the car?