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Running wires through the firewall

This is a discussion on Running wires through the firewall within the General Help forums, part of the LSx Technical Help Section category; I understand that beneath the PCM there is an access to the interior of the vehicle for wire runs. The ...

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    Running wires through the firewall

    I understand that beneath the PCM there is an access to the interior of the vehicle for wire runs. The problem is that for everything I have done to our car, it is on the wrong side of the engine bay. I really dislike stringing wires from one side of the car only to come back across to get where I need to go. Therefore, all my wire runs are through the firewall directly into the driver compartment.

    The best place to do this is just above the firewall wire harness connector, which is located to the right of the brake booster (viewed from front of car). There is an area there that is easily accessible from inside the vehicle after dropping the panel beneath the steering wheel and the padded inner panel above the footwell -- 4 screws, 1 wire connector and 2 push pins to remove everything. In this picture, the gray wire is for my line lock that was previously installed in the same manner.





    To make the holes, I started with a center punch slid into a 3/8" deepwell socket that I use electrical tape to secure. Using a towel to protect the wheelhouse, a couple of 3/8" drive extensions and a hammer are enough to make a divot in the firewall to start a drill bit.








    From the hardware store, you'll need a drill bit extension (around $10-$12) and I also used a long bit for the first hole (around $6-$8). The starter hole is 1/4" and it does help to have a nice sharp bit. The firewall is actually fairly thin gauge metal so it doesn't take much to punch through. You only want to pierce the metal and the thin plastic liner in the footwell that rests against it. Don't go more than an inch or so through as there is an electronic module of sorts in this area.








    Once the first hole is drilled it is easy to enlarge it to whatever size you require for your wire run. You will need a bit with a small shank to go larger than 1/4" -- these I had so I am not sure of the cost. The holes were drilled out to 3/8" for my LC-1 and fuel pressure gauge wiring runs. Rubber grommets were installed to protect the wiring from any sharp edges.

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    Smiles for 9.5 Years cammed goat's Avatar
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    Very nice Jeff.

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    Thanks! I don't recall seeing a write up on this before so I thought it would be nice to post up some pics to document it.

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    Is this more for "A" piller gauges then?

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    Quote Originally Posted by bsteff View Post
    Is this more for "A" piller gauges then?
    On our car, it is both gauges and a line lock.

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    I put this by the lc-1 install in the stickies since they're somewhat related.

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    Great job, should help some people out. Getting a hole drilled back there is pretty dang tricky, Thanks Jeff.

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    Thanks guys! It just seemed the easiest way to get where I needed to be. The LC-1 controller ended up right under the brake booster, away from the headers and shielded from moisture if we ever get caught in the rain.

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    I am in the midst of swapping out wideband air-fuel gauges in our car and had to run a new harness through the firewall. Fortunately, in most cases the wire ends are removable from the connectors and this allows for the harness to be passed through the firewall without cutting and soldering it back together. The connector for the new wideband gauge is just about 5/8" in width and that would make for a sizeable hole to shove it through the firewall intact. I found in this case that it was easier to remove the wire ends from the larger connector into which the O2 sender plugs and ran the wires from the driver compartment out to the engine compartment.

    The first thing you need to do is make a record of the wire placement in the connector to ensure that it is properly reassembled. I simply took a picture of both sides of the connector with my camera. Although I have a tool for removing wires, the ends didn't match my connector so I had to improvise. A standard size paper clip was unbent and then cut to form a U-shaped tool. Inserting this into the face of the connector depresses the tabs and allows for each individual wire to be extracted. As this is a weather-pac type connector, there was also a plastic retaining cap onthe back side that was unclipped and removed.








    Once all the wires were removed from the connector, it was fairly easy to push the individual wires through the hole I had previously drilled. I shoved the first 3 or 4 through and then from the engine compartment pulled the remaining wires through. I slipped a rubber grommet over the wires and ran it up to the hole in the firewall where it pressed into place. This is very important as the wires would otherwise be prone to chafing on the sharp metal edge of the hole. The wires were then reinserted into the connector and the plastic cap was clipped back into place.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Jeff, this worked like a charm. So much easier then running the long way around.

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    Glad it worked out for you. I just finished up the last of the wiring for the new wideband and tested it out. Works great so far, but it'll be another 3-4 months before I am able to drive the car again to see how it acts with the cutout.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Throw her on that nice lift you got and test it that way. Just raise it enough to get the tires off the ground and open the cut out should be enough.

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