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

Thanks, this thread got me thinking and I started a search for such devices and I think I found my solution, although it is expensive. Take a look at JEG's site for firewall grommets. These should work great for my hoses but you could cut one on the rim at one of the four bolt holes and then cover the cut in the rim with a chrome/stainless washer; put the cut on top so the wires rest on the uncut part of the grommet.

http://www.jegs.com/p/Earl%27s/937113/10002/-1/10603

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

Originally Posted by Don Shillady

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

Don,
My bulkhead fittings came from Yogi's in Iowa and are Vintage Air. A lot of suppliers have them Also, Billet Specialties (http://www.billetspecialties.com/pro...?cid=7&scid=84) have several different versions. Again, Yogi's for Billet (http://www.yogisinc.com/results.cfm/...14/product.htm)

For a nice looking firewall grommet for my throttle linkage, I just used my 2" hole saw, cut a piece of .125 aluminum and then made the center hole with my Unibit to .75. I then put a piece of slit urethane behind it as a seal (this was C9's suggestion though he used Teflon) This would be a good way to do wiring as well - the neoprene will hold the wires nicely - I may have to change to something more slippery (Teflon or similar) for my linkage

Well, I went out and looked last night at my wires/hole again. The wires are CRAMMED in there. Tighter than I thought as there is NO room at all to work with. One thing I have going for me is that the hole that the wires go through now is actually NOT on the firewall. It is just below the firewall where the floor meets the bottom of the firewall so you really can't see it. You can only see a group of wires going to it.

This is a fiberglass body. I think the Dremmel tool (mine has low and high speed) may be my only option in trying to outline the existing circle and making it larger.

If that does not work I was also thinking I may be able to disconnect 5 to 10 wires (choose the easiest one's to deal with), cut the end connections off and pull them through the body. Hopefully that may give me enough room in the hole to use a file or again try a Dremmel Tool.

Also something I found that may help spark Ideas. Check out the "split grommet seal" at the bootom too! - http://www.sealsit.com/firewall.asp

Originally Posted by bucs012

Well, I went out and looked last night at my wires/hole again. The wires are CRAMMED in there. Tighter than I thought as there is NO room at all to work with. One thing I have going for me is that the hole that the wires go through now is actually NOT on the firewall. It is just below the firewall where the floor meets the bottom of the firewall so you really can't see it. You can only see a group of wires going to it.

This is a fiberglass body. I think the Dremmel tool (mine has low and high speed) may be my only option in trying to outline the existing circle and making it larger.

If that does not work I was also thinking I may be able to disconnect 5 to 10 wires (choose the easiest one's to deal with), cut the end connections off and pull them through the body. Hopefully that may give me enough room in the hole to use a file or again try a Dremmel Tool.

Also something I found that may help spark Ideas. Check out the "split grommet seal" at the bootom too! - http://www.sealsit.com/firewall.asp

My fix - cut the wires, install flat multi-wire connectors, make the hole bigger, install a grommet, reconnect the wires. A heluva lot easier then trying to do a work around with a Dremel tool, a modified file as I suggested before I knew it was that tight. I would consider doing the connectors below the floorboards with water proof connectors so you could lift the body if so inclined later i.e. a fresh paint job. Search EBay.

What do the flat multi wire connectors look like? This sounds like a good winter project!

Originally Posted by bucs012

What do the flat multi wire connectors look like? This sounds like a good winter project!

Something like this though you do have to make sure that your car wire gauge is the same as or smaller then the connector sizes. That is, if you have a 16ga wire, you need a connector that will be for 16ga to possibly 12ga. Remember, the larger the wire gauge number the smaller the wire. 18ga is smaller then 16, 14 and so on.

Probably the connector idea is good; anything is better than trying to cut a clean hole with that Dremel tool in my opinion with the added problem of possibly cutting the insulation off the wires with the Dremel. I have made a few cuts I wish I could take back but cannot! I have also been measuring and searching for bulkhead fittings as IC2 suggested. The rubber ring grommets I showed above are 3" in diameter and a bit too big for my installation and the ones that IC2 used are spaced too close together to match up with my existing holes with a 2 1/2" spacing on 1 1/4" diameter holes so I am back at either making my own bulkhead plate from aluminum and getting it polished locally (possible) or making use of the VintageAir rubber grommets. Looking it over and measuring again I think I will try to use the rubber grommets I have with a little grinding on the inside to make the 'glass thinner around the hole. I think I can use a lawn mower sharpening tool to grind away some thickness of the inner wall so that the narrow groove of the grommets will seal correctly. The small round tapered stone will maybe grind away some of the thickness. Again thanks for the discussion of what may be a problem that is more common than one might suppose!

Don Shillady
Retired Scientist/teen rodder

bucs012, Thanks for the link to the Seal-It folks. I ordered two of the 2" diameter grommets at $16 each AND "Arnold" on the tech line will cut out the holes for me at 3/4" which should give a snug fit for the 7/8" heater hose. It turns out that after cutting the holes three times, ever larger, to fit the Vintage Air grommets, I now have 1 3/8" diameter holes but the 2" Seal-It grommets will still cover the holes and four small bolts should firm up the fit and I can still jockey the positions for a nice look along the edge of the firewall. All I can say for the original intent of this thread is that if you cut the wires and go with the connectors IC2 suggested, you could use a hole saw instead of a Dremel to enlarge the hole for a new grommet. The way I did it (twice on each hole) was to angle the hole saw into one edge of the hole and let it cut into the other edge gradually. This may offset the center of the hole a bit but in the floorboard that probably doesn't matter since you say it is hardly visible now. Hey, if I ever get my car on the road I will owe thanks to MANY of you, this site is extremely helpful to me!

Don Shillady
Retired Scientist/teen rodder