Ok, for simplicity mabye we'd better go with using a plug in supply for the relay coil. From here:
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the
AC/DC UNREG PLUGTOP PSU 12V DC 300MA RC code 85-2913
is fine for 12v relays such as:
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32.21 12V DC MINIATURE SPDT 6A RELAY RC code 60-4087
You then use the switch output from that board to switch the current from the plug in supply into the relay coil. This will close it's contacts and, with the external drive connected through them, switch it on.
This shows how to connect up the relay. It is a PCB model and will need to be soldered. If that is an issue, you could use one of these with push on connection:
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Anyhow, this shows how to connect up the PCB relay:
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I attached a diagram which should help. The only thing i'm not sure on is that board and how it's outputs work, so this may not be everything
. I'm treating it as a switch, but don't think it's as simple as that.