Drilled out the tooling hole in the firewall to 29mm to accept the grommet for the wiring loom pass through.
Made a bracket from 25 thou to mount the regulator plug securely.
Routed wires within the engine bay, trimmed, neatened and tied off the loom and fed it through the firewall grommet and sealed the wires as one with heatshrink with polyurethane sealant oozed inside the heatshrink before shrinking.
grommet fitted to the firewall with polyurethane sealant
zip tie holds the plug in the bracket to aid keeping the wiring tidy
loom to be sealed to the grommet with a silicon washer around the wires and glued with polyurethane
