I have been toying with building aluminum plug/grommets to seal the factory holes and still allow smaller cables to pass through. The piece would overlap the hole by 1/8 inch. The back side would have a shoulder that would be cut to fit through the hole and a thin o-ring would seal the hole from the engine side of the firewall. The disk would be drilled to accomodate the wire or hose that passes through and also partially drilled and tapped for two screws on the back side. A backing plate with a pass-through hole and two screw holes would mate to the disk on the driver's compartment side of the firewall.
Sorry. Here's a crude drawing. Polish, brush, annodize, engrave, clear coat or whatever. A rubber grommet would seal up the center hole around the wire/hose.
I came up with this idea because I am replacing my wiring with a painless type system and I don't want to weld up the factory holes, but want it to show nicely.
