Here's how you can make your texturelight switchable (Requires ZHLT 3.4):
Turn your light fixture into a func_wall, which i believe is already done.
Open its properties and name the brush. Now select Grouped in the Texture Light Style property. If this property does not exist, you can add it manually by turning off SmartEdit, and adding these keyvalues:
Now create a light entity with the same name as the brush entity. Hlrad will now pretend that the light emitted by the texlight is "really" being emitted by your light entity. In other words, turning the light on and off will now turn the texlights on and off, too.
You'll probably want to set the brightness of the light entity to 1 1 1 0.1, so that it emits no light of its own (this trick is unnecessary if you're using Spirit of Half-Life, which supports switchable texlights directly).
If you hit Alt+P to check for problems, you'll notice one or more invalid keyvalues errors. Just ignore it, this happening because the Texture Light Style property is missing from the FGD that you're using. If want to fix this, find the func_wall FGD code and replace it with this code:
@SolidClass base(Targetname, Appearflags, RenderFields, Global, ZHLT) = func_wall : "Wall"
_minlight(string) : "Minimum light level"
style(choices) : "Texture Light Style" : 0 =
0 : "Normal"
-3 : "Grouped"
10 : "Fluorescent flicker"
2 : "Slow, strong pulse"
11 : "Slow pulse, noblack"
5 : "Gentle pulse"
1 : "Flicker A"
6 : "Flicker B"
3 : "Candle A"
7 : "Candle B"
8 : "Candle C"
4 : "Fast strobe"
9 : "Slow strobe"
12 : "Underwater"
If you're confused about this, ill do it for you, just send the FGD to me and ill send it back to you.