I assume you are referring to the 'ground wire to bridge' in the diagram. That wire is there to ground the strings when using a magnetic pickup. It's not necessary when using a piezo.
If you are using a bolt as a bridge, you can drill a small hole under the bolt for the wire, strip the end of the wire and spread it so it is in contact with the bolt. If you want, you can apply a little solder to keep it attached but the string pressure should keep the bridge in contact with the stripped wire.
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Ted Crocker said: