This has happened to me too and my symptoms were the brake lights staying on in drive, neutral, reverse (with engine running), and also no high bar brake light at any time. The brake lights were okay, initially, when in park.
So I opened up the umbilical harness as described, using the hidden tab, and immediately saw lots of wires with cracked casing. In my case the thin green wire with yellow stripe was completely broken apart, and I know from checking the bulbs on the high bar brake light that this wire goes there.
I connected the broken wire and all problems were resolved. e.g. side brake lights started working normally and also the high bar light also began to work again.
So it will be interesting to fix this mess - wish I could shrink wrap them, but it is a tight space and the rear windshield washer feed line is also in this same umbilical, making it tight and need to be careful not to puncture that hose.
Also, everyone should note that abnormal hot temperatures that can occur in the side brake light assemblies. As double filament brake light bulbs burn continuously while driving, the danger of melting the plastic taillight red lens is high. Mine were hot too touch !
Thanks all for this great post as it pointed me to the problem area quickly. To bad they did not engineer this better for real world use - it is clearly a weak spot, which can cause some interesting problems.