Many thanks for the reply 
I’ll give that a try.
Your pictures are missing information about the flash drive.
We have to analyze the circuit with the flash drive connected.
Otherwise, there is no circuit.
The general rule for shielding is still the same
The shield has to be connected to ground only on one side.
Connecting the shield on the host side to the power ground is the best.
Connecting the shield on the device side to the digital ground is acceptable.
Internal connections of the flash drive have to be taken into account.
That’s correct.
This is a safe connection that will work with any flash drive.
That is not the best because the shield is connected to the digital ground on the device’s side.
That is ok, but it’s not the best.
If the flash drive has an internal connection between the shield and the ground, the connector and flash drive itself are not actually shielded. The outer shell of the connector is just another ground connection.
In this picture, the shield is not connected to anything.
It will work if the flash drive has an internal connection between the shield and ground.
But it still won’t be the best solution because it’s not grounded to the power ground on the host side.
The best solution is the last picture, with the shield connected to the power ground and the flash drive that does not have a connection between the shield and the ground.
It will create a shield connected only on the host side to the power ground over the full length of the harness.
Thanks for the reply.
My USB stick has an internal connection between the ground pin and the shield (the same as my USB adapter).
So which should I use?
I had wired it as per my 1st drawing ‘Safe connection’
So can you please clarify, which way is now best?
I had already wired it but have now taken it back out of the car as I want to get it right before I put the dash back in (a lot of work).
Please can you advise.
So this should work ok, right?
What are the implications of having the ground pin connected to the shield? I don’t want to cause other issues.
Assuming you use a flash drive with an internal ground and shield connection.
The best connection method:
Everything from the ADU up to the flash drive is shielded.
The shield is connected only on one side (device side).
The shield is grounded to the digital ground (inside the flash drive).
The safe connection method:
The harness from the ADU to the USB socket is shielded.
The USB connection and flash drive are not shielded.
The pro of that solution is that it will work correctly also with a flash drive without internal shield termination.
- The digital ground of the device is the return path for the noise instead of the power ground.
- The shield termination is on the device rather than the host side.
Those are not critical.
They are just not optimal.
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Thanks for the reply.
I did the wiring yesterday and opted for the following:
The USB stick ground and shield are connected together at the USB stick.
Hopefully it’ll work ok.
In that case, you have a shield connected to ground on both ends.
One side is connected to ground at the ADU end.
The other side is connected to ground inside the flash drive.
That means there is no shield.
Either remove the shield connection on the ADU side or change the flash drive to one that doesn’t have internal shield termination (flash drives with fully plastic connectors are like that).
Yes, that is also ok.
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Many thanks. That’ll much easier to access now the wiring is finished.
I have the following pendrive: DataTraveler Kyson USB Flash Drive – 64GB - 512GB - Kingston Technology
I can assume, with this design there is internal connection between ground and shield? 100%?
Based on this, I should use the first drawing from your May 26th post?
does it even matter, if it’s literally 5-10cm between ADU connector and the green connector for the USB?
currently I use just an old PC rear usb card connector spliced with 4 pins to the ADU, without shield cable. Sometimes it stops working. I figured maybe the very thin cables with the big terminals in the connector are not great. but every time I just disconnect the main ADU connector and reconnect it, it works fine again for X amount of time. Is that some shield/ESD issue currently?
No. There may be no internal connection.
And according to the USB standard, there should be no connection (termination on the host side).
You must confirm this or use a safe connection method (shield termination at the receptacle).
If it has the connection, yes.
And if you use the same type of receptacle as on the drawing.
Depends on what’s close to that part of the harness.
If there are engine or power supply wires nearby, they can have an effect.
It may be an ESD/EMI issue.
It can also be an intermittent connection.
The best solution is to use a receptacle like the one in the picture, which allows you to use your own wires. Alternatively, to ensure a good crimp with the thin wire, add a piece of thicker dummy wire specifically for the crimp section.
As far as i know anything above 32gb is not possible natively format for fat32. You have to use 3rd party software for it and sometimes can be troublesome. So personally im not using bigger than 32gb