I think the guy makes it look more tricky than it actually is!

Cut the pump feed wire, fit the relay's load connections across the two ends, find a suitable ignition switched feed, run it to a switch via a fuse and back to earth through the relay's trigger terminals.

You can choose to either fit a relay that is ON when 12V is a fed to the trigger, or one that is OFF when the trigger is switched. Therefore you can decide whether you want the ABS to be active by default, or disabled by default. Might be useful if something went wrong with the relay circuit if the relay was one that has continuity between the load terminals when there is no power at the trigger?

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