I have a 1989 Honda Accord that I would like to wire a 4 channel amp under the seat. I have all the wiring figured out... except getting through the firewall. It seems to be a dual insulated sort of deal. There's the engine sheet metal, then there is insulation in the middle, then the dashboard sheet metal. How do I go about getting through this? I want to wire a 4 gauge wire to the positive terminal with a 30 amp fuse on the wire. There is ONE plug available on the firewall of the drivers side (a manual choke would have gone here) but since I have an automatic choke, it is unused. How do I get through to the other side without puncturing anything important? This is not described in the genuine Honda repair manual, so I have no idea what may be between there. Any help is appreciated, thanks for reading!

 

I have had this problem before in non Honda vehicles. The best advice is to BE CAREFUL when drilling blind. If you can see the plug hole on the engine bay side, then try to figure where it will enter into the cabin.

If you remove the plug and clear away the insulation material, try to get a center punch in there and tap it with a small hammer. Then look for the dimple on cabin side of the firewall.

I doubt that the manufacturer ran wires or other lines in the void between the inner & outer walls but Im sure that many pass through so be sure you can see both sides of the inner wall before you dimple it.

Once your confident that you will not damge anything drill the appropriate size hole.

A few things to keep in mind; after you drill the hole besure to put some edge protection around both the inner & outer holes so that the sharp edge of the metal does not cut your wire. If you are using large AWG, the bend radius of the wire will also be large. Check the area around the inner hole to be sure that the cable will not interfere with the gas pedal, brake pedal etc..

A drill stop is a good tool to prevent you from drilling too deep. Its like a collar that fits around the drill bit and can be tightened down at any point on the bit. set the stop shallow and you dont have to worry about going too deep and damaging something on the other side.

Hope this helps!

 

Drill your hole there.

If the car was a 5 speed, that is where the clutch assembly would go through.

Double check to make sure it is clear on the engine side.

 

DOUBLE check EVERYTHING before you start drilling! and you should be all good! Good luck! =D