Thread: Running wiring through firewall

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I have a Fiberglass 32 I just bought and the car has been together a few months. The guy built the coupe and I noticed he drilled a hole on the passenger side of the car BELOW the bottom of the firewall and ran all the wires through that area. It's about a 3/4 to 1" hole.

I noticed he did NOT put a grommet or any cover over the group of wires running through so they are pretty tight against the fiberglass hole.

1. Is there any creative way I can make this hole larger (without removing all the wires) so I can put a grommet in the hole or run some wire loom to protect them?

2. Is this the normal place to run wiring through?

3. Since I am new to rods, any pictures or explanation of how you guys did it, would be great!

Thanks much!

Too bad the builder was in a hurry and/or didnt care! You have probably seen the rubber grommets that can be split with a knife and installed around a bundle. However, if the wire bundle fills the hole, there is no room for a gromet. Short of removing the wires and doing it properly, the only temporary solution is to use a piece of thin metal wrapped around the bundle and slid thru the hole. Secure the metal wrap with cable ties or tape...looks like crap and is hokey but it just might keep the wires from being cut until you can remove the wiring and do it correctly.

If you have access to a machine shop, you can fabricate a split collar that is smooth in the wire contact area. The collar would be four pieces and two would install from each side to isolate the wires from the raw fiberglass edge. The four pieces would have holes to go thru the firewall and bolt the assembly together.

mike in tucson

If your firewall is 'glass, and if you can shove the wires around a bit plus protect them with some good tape, you might be able to get a file in there and enlarge the hole for a split grommet. You can thin down a file and remove one side of the file teeth on a grinder. I grommeted mine plus added this from Watson's Street Works(http://www.watsons-streetworks.com/aluminum_trim.html)

It's kind of PITA to install - I made up studs instead of using their machine screws and made a steel drilling template based on their paper version (which is off a bit dimensionally)

Use a Dremel to cut around the out side of the hole so you end up with a bigger hole in the firewall
Then slice the piece left around the wire to get it off...

MM64

Great ideas, guys. I know I can undo all the wire wraps around them that are now running across the top of the cab, over to the corner and down the side to the floor. That will give me LOTS of room to at least mark where the wire go thru the floor, then at least wrap them in tape or something for now.

I am going to see if I can pinch/squeeze/beg/curse them together tight enough that I can file or use a super fine dremmel tip and make the hole larger. Very slow and careful! I at least want to get a rubber grommet in that hole.

Best case scenerio I will be able to do all this without have to take 5 or 10 wires loose to gain enough room to work with.

Thanks for the tips!

I have the same problem running hose for the heater through the firewall. I see IC2 and some others seem to use bulkhead plumbing but I did not know where to get that sort of metal tubing interface. I am open to suggestions for a source of those nice looking fittings but I have already been through several hole enlargements and have been able to use three ever-larger hole saws. I could still install a metal bulkhead with tubing fittings to cover the holes I have now. A complication you did not mention is that the 'glass is much thicker that would be the case with a metal firewall and I have also been through two sets of rubber grommets which really do not work because the groove in the grommet is not wide enough to accomodate the firewall 'glass which is about 3/16" to 1/4" thick. I would also warn you that it is not easy to cut around existing wires and I was lucky to be able to run a larger hole saw through an existing smaller hole (twice). I have used a Dremel tool to clearance my 'glass body in several places and it will cut fine BUT you better have a steady hand because the twist of the cutting bit makes it more difficult to control the path of the bit than it would be to just draw a freehand line. If you choose this method I recommend you practice on some scrap fiberglass for several attempts until you think you can control the bit. Thanks for this thread, it gives me the idea that I can use one of those bulkhead tubing fittings for the heater hoses if I can find out where to get them. However in your case I think the best choice is to find or make the multipart bolt-together metal or plastic grommets, the 'glass is too thick for most rubber grommets. The idea of a wrap around metal sheath may work pretty good if you can hide the seem on the bottom and put the fastener on the inside of the firewall. My main message is to not be very optimistic that you can control a Dremel cutting tool in a way that will lead to a finished appearance. Good Luck and thanks for some ideas from others.

Don Shillady
Retired Scientist/teen rodder

hay bucs try putting a screw type hose clamp on both sides of the firewall you may be able to squeze the wires together enough to get a dremmel or file in there hope that helps ted