New brake light switch or not, you need to understand how the switch is activated. As mentioned above, the hole in the shaft from the HB needs to be elongated as it fits on the pin from the brake pedal arm. As you press on the pedal, the first little bit, the slop of the pin in the hole, is what activates the light switch. It's awkward to lay under there and see how it works, and if it's working properly.
And, yeah, I mangled the clip and had to put on a new one, too.
2004.5 Silverado 3500 SRW 4x4, D/A (LLY), Ext. Cab, Long Bed
engineer837 aux rad, TxC CAI, LBZ MP, Scangauge II, Nicktane aux filter head, KD lift pump, 2008 PS pump, 2011 hydroboost, Frederico Swaybars, Rancho 9000XL, Torklift StableLoads, BFG AT/KO2, Lance 835 Camper often in the bed.