Sometimes you can use the holes which are already in use by other wire
bundles. Remove the electrical tape on the engine side of the wire bundle
on the firewall right where it goes through the firewall where it connects
to the grommet. Give your new wires a light coat of silicone grease at the
end to help get them started through the grommet of the wire bundle. Note
that you'll be forcing this wire along the side of the existing wire bundle
and not through the middle of it. Once you get the wire through, you can
carefully pull it out to the length needed. Clean off any silicone grease
which remains near the firewall grommet with some contact cleaner, let it
dry, and then rewrap it with some fresh electrical tape to help seal out
water from getting through the grommet.
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