The important thing to know about penetrating a firewall is resealing it. Anything that runs through the firewall must form an airtight seal as it penetrates the wall. If this seal is damaged or not maintained, fire and smoke in the engine bay can more easily reach the passenger compartment and its occupants. This seal must be maintained in order to give passengers more escape time in the event of a fire in the engine bay. Running an amp power cable for subwoofers is no exception. The cable must penetrate the firewall and maintain an airtight seal.
Locate a vacant area on the firewall and determine the hole size needed for the grommet. This is usually denoted on the grommet package. Verify that the amp cable fits inside the grommet's center hole tightly.
Drill the hole in the firewall. Drill very carefully to avoid damaging any wiring that may be on the other side of the firewall.
Insert the grommet and work it until it fits tightly inside the new hole. Check the grommet on both sides of the fire wall to make sure it is seated correctly. Push the amp cable through the grommet's center hole slowly. It is helpful to use a light lubricant on the cable to avoid damaging the grommet.
