Passing a lot of wires through the firewall

Discussion in 'GM Electrical Tech' started by Crawdaddy, Jul 26, 2012.

  1. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    I've been thinking about this issue for quite some time and I haven't been able to think of a good solution yet. I have been working on installing various electrical bits (gauges, alarm, lights, a/v gear, etc) in my Suburban. Because it's so many different items with wires that need to go through the firewall, I don't know how I'm going to run it all through and still maintain some form of water and wind resistance. Off-hand, I need to get 2 runs of 1/0 power cable or larger, 10 or so 18AWG wires, and 3-4 12 or 14AWG wire through, so it's a lot of wire!

    I've been thinking for the smaller wires that are mostly for gauges and such, I could use multi-conductor sprinkler wire or the like with terminal blocks on each side to break it out, but I've only seen 7-conductor 18AWG sprinkler wire. I still have some heavier gauge wires that need to go through and of course the monster power wires. The 1/0 wires I've been considering running under the cab to under the 2nd row bench seat where the floor takes a 90-degree jump up for the bed area of the cab, but I would need some very good waterproof bulkheads for that.

    Any ideas on getting massive amounts of wires into the cab?
  2. zigger215

    zigger215 Member 2 Years 500 Posts

    Are you running these wires to various points under the hood? Or are you running them to power only? I would say to try and use distribution blocks in the cab itself. Your best bet would be to design your system in a way to minimize the actual number of runs out of the firewall rather then to figure out how to run a huge number of things out. Doing this would also clean up the install. If you don't mind, list off the purpose of each conductor, I can give better advice with that being known.
  3. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    A couple tricks I learned aboard ship for running cabel runs and wires from exterior to interior were:

    Drill your firewall hole then fasten a flat piece of rubber over the hole, fasten it with fender washers to help keep it slightly stretched and sealed on the edges, make a small slit in the center to pass your wires through, small enough so the rubber has to stretch to pass the wires.

    Next method is using a portion of an inner tube make a sleeve about 6" long to attach on the inside of the firewall, pass through the firewall and route wires through.

    If you have a real water intrusion problem you could use a combination of the two, but I've seen both methods hold out water in gale force storms so I think they should be sufficient for what your doing.

    We also used fittings similar to "glad packings" with rubber in the center and the more you tightened them they squeezed the rubber tighter around the cable runs to make a water tight fitting. (These last fittings would seal out water upto a couple hundred feet, they still use the method on Submarines when going from interior to exterior or water tight compartment to water tight compartment).
  4. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    First, I have my gauges, so I have sender wires for tach, trans temp, oil temp in the future, possibly another gauge or two. Each one of those will typically take 1-2 conductors going into various parts of the engine compartment and can't be combined. The actual power for the gauges and gauge lighting will come from under the dash. Next, I have switches for front and rear auxillary lights. The switches will just switch relays so they're not high-power and the source of power for the "manual on" side of the switch will also come from under the dash, but I also have trigger lines coming from the reverse light switch and the high beams, so that's another 4 conductors. There will also be a few wires for the alarm and remote start. I don't know how many, but I'm sure it'll be somewhere around another 4. There will also probably be some other electrical control lines I'll run through for a battery isolator control and other things I don't yet have so I'll want to pull spares for future expansion.

    As for the main power lines, I'm going to use either 2 or 4 1/0 welding cable lines for the main power feed for my radio, amplifier, ham radios, cb, inverter, and other electrical goodies I have in and around my center console. I'll use a distribution block or two in the center console to break the main power feed out to the various aformentioned high-power goodies.

    So yeah, I have a lot of non-combinable lines....
  5. zigger215

    zigger215 Member 2 Years 500 Posts

    Run a single run of 1/0 into the cab into a distribution block and from there durn 4awg out. That will be PLENTY of upsizing for your high powered equipment. Trust me on that

    Second. Your auto start, get the tach signal from behind the cluster, don't run a hood pin (no point, they are designed because shops need a fail safe to protect against injury law suits), you will only be running a single 18awg wire out into the engine bay for your siren, ground the siren to the outside firewall. Your sensors have grounds, ground them to the outside fire wall. By my estimate you will be running only two wires ours for lighting (front and rear). A single wire out per gauge, a single wire out for your auto start, a single 1/0 for big power demand items. What gauges are you installing and what year is your truck
    Last edited: Jul 26, 2012
  6. Enkeiavalanche

    Enkeiavalanche Loving the Outdoors Staff Member 5+ Years ROTM Winner 5000 Posts

    Jl Audio and a few other 12 Volt Co's make a Good 9 conductor wire. I used it for the lights in the back of my truck..

    As for Welding cable Is it Flexable? I would just stick with 12 Volt 1/0 Ga..
  7. zigger215

    zigger215 Member 2 Years 500 Posts

    I second everything enkie just said. 9-conductor wire is great for your situation
  8. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    Cool. I didn't realize JL made 9 conductor; I'll have to check that out. Welding wire is the same as 12v car audio wire but with a solid black jacket and not as large of a price tag. It's thin-strand copper.

    As for the main feed, I think 1/0 won't be enough for me once you add up a 1500 watt or better inverter, 1000 watt amp, a 100 watt ham radio, another 50 watt ham radio, and anything else I put on that line. By my estimation, that's over 200 amps right there, though I won't neccisarily be using it all at once. I mentioned 2 runs because I'd also run the ground all the way back to the battery. I know you typically ground to the frame, but with that much current I think it's better to make a nice short, heavy path to the ground.
  9. Enkeiavalanche

    Enkeiavalanche Loving the Outdoors Staff Member 5+ Years ROTM Winner 5000 Posts

    Do you have the Amp draw on everything you are installing? Are you upgrading the Alt and Batt's? Ground wires and power off the Batt and Alt?
  10. zigger215

    zigger215 Member 2 Years 500 Posts

    Don't run back to the battery with your ground. Ground RIGHT next to all of your equipment. We urge customers not to run the ground back to the battery. One run of 1/0 will be plenty for your equipment still. Make sure it's 12volt cable, it allows more current flow then welding cable in a DC circuit. I have a 5,000watt competition system and my grounds are right next to the equipment and I'm feeding the entire system with a single run of 1/0 without starving anything.
    Last edited: Jul 26, 2012

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