If it's not detected by the BIOS, regardless of how it's formatted, then the drive controller is dead. This implies:

- overvoltage
- shorting electronics against the sled
- overheating
- extremes of low temperature

You mention your car has electrical problems: are they due to overvoltage?

Have you thought about returning the drives under warranty?
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One of the few remaining Mk1 owners... #00015