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Best place to drill body for cables?

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Got a 2015 GMC crew cab that is getting a lightbar and other emergency equipment installed. Trying to think of the best place to bring power and other cables into the cabin, preferably in the rear passenger side. Need at least 3/4" I would say for 8 ga power, lightbar cables, and everything else.


I've been looking all around it and it doesn't look easy. Passenger side underbody has virtually nothing to cable tie onto so will probably need to drill clips to the frame or something. Any suggestions?

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If you want to bring the light bar cable in through the roof bring it in through the third brake like then notch it and silicone. If you want to bring it in the rear under carriage use a cab vent or something similar I will climb under one today and let you know what looks the easiest

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I ran 2/0 into the cab by running a 3/4" flex conduit from under the hood, among the frame/body, then punched up through the floor back by the jack. (Crew Cab.) I posted pics in the audio thread that is linked above... it's a few pages after that post. I can snag a few more pics if you'd like, just let me know.

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Avoid drilling the frame. Use clips. GM Upfitters manual specifically states: "Do not drill holes in frame flanges"


Holes for mounting brackets must be drilled in the vertical web of the frame.

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Thanks guys, got it done and it was easier than I thought! I have a pile of pics I'll post later. Basically I did it this way:


Parallel to the passenger rear seat bolt about 8" away, and perpendicular to the jack bolt about 3" toward the front is what looks like a 2" knockout in the underside of the body. Single hull sheet metal. Landmarked, center punched, pilot hole, then opened it up with a step bit.


Cut away some of the carpet in the cab and reamed to about 1 1/8" to fit a 1" threaded PVC conduit bushing. Had another person place and hold the lock nut in the cabin and threaded the bushing in from the underside. Boom, nice smooth 1" hole that's perfectly protected. Did not silicone around the bushing, should not be necessary as it's quite well protected from the elements. This install is also quasi-temporary as I'm awaiting other equipment.


The lightbar was mounted using Towman-style brackets to Dee Zee no-grill bar, drilled straight through. Fished the cables through the hexagonal tubing (what a pain that was), exited at the base, loomed and dropped between the box and cab. A single loom clip keeps it from rattling, then over the frame rail and into the bushing.


Power was connected to the VERY lovely, upfitter-friendly power distribution block on the battery, fused with a 40A maxi fuse, and 8ga loomed and dropped down to the frame rail. Since there are absolutely NO cables you can conveniently cable tie onto on the passenger side, I fished the frame rail from the nearest holes at either end and added a single loom clip before the bushing.


Finished the temporary board with a Whelen amp/control box and the WeCan lightbar controller, tidied it up and ran the remote around the back seat, under the sill plate, behind the driver's seat and mounted the remote clip to the console side with 3M VHB tape.


Overall I found it easy once I knew what I was doing, took an evening and morning to finish. I'll post the pics later.

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Ok I don't know why we can't edit posts, so I'll add these in a separate one.


This is the location from the underside where we chose to come up. Note the large "knockout" looking area (which isn't a knockout, just single hull sheet metal). Orientation of the photo is top is to the front of the vehicle, bottom towards the rear.




Passenger side under the seat where it comes up, about three inches in front of the skinny bolt holding the jack way behind the seat.




We are drilling here to make room for this guy:




The "knockout" was center punched from the underside as it's difficult getting a drill in there, then a small pilot hole was drilled bottom-up to landmark it in the cab. Once we'd poked through, a bunch of the carpet was cut away with a sharp knife and hogged out to make room for the step bit (hole saws are garbage). The step bit was chucked up into a 90 degree drill and the remaining hole was drilled out from inside the cabin.


I got one person to push the lock nut through the carpeting and oriented properly around the hole while I threaded the PVC bushing in from the underside. It was hand tightened to the point I couldn't unscrew it. Sucker's going nowhere. Now we have a generous, heavily protected and smooth hole in which to run any wires we desire. These bushings are available at Home Depot in a variety of sizes and are a buck or two. Way better than any grommet.


The 8 gauge power wire was connected to one of the battery terminals and dropped down to the frame rail, then fished through here:




And brought out here:




A single clip was added to the frame to keep the loom from flopping around and then up into the cabin:






The lightbar:




The Dee Zee bar was drilled and the cables fished through on the passenger side (factory harness location for the lightbar) and brought out near the base:








We dropped it down between the cab and box and it needed only one loom clip to keep it secure. This was drilled in a single-hull location and not into any blind areas (camera orientation is vertical; this is the back of the passenger side of the cab):




A work in progress...




Done! Just routed the CAT5 around the back, under the driver side rear sill, and to the controller at the driver's seat.



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