Battery relocation/ NHRA kill switch/MSD 6AL Wiring help needed.

Or same concept as above with both wires through a grommet like a 'fleet' alternator wiring setup.
In this case the guy was planning on an engine compoartment and a trunk battery, but of course still needed to cut off power from the trunk.
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Mattax, how is the relay interrupting one of the field wires better than simply using the small posts on the disconnect as the interruption point?