Meansse

I have a 2021 Silverado 1500 duramax and I have tried both driver and passenger side cutting off that nipple, which allowed me to fish one small 14awg wire through, but could not find on the cab side. No idea where it is going, but nowhere I can access. I purchased a light bar harness and need a decent size hole to fit the connector through. I do see a little room near the emergency brake cable, but not any room to drill and not much clearance on engine compartment side. Why is this such a hard task? I’ve spent a lot of time trying to get wires through and hoping I haven’t nicked any wires on either side where those bundles go through. Thanks for any advice.