ford explorer headlight stereo dimmer

I have a 1993 Ford Explorer which I just took to Car Toys to get a JVC KD-AHD59 installed in. Everything works fine (except that I seem to have a blown speaker, but that's a separate issue), but the lights of the stereo are supposed to dim when you turn on the headlights. It doesn't, and it's very bright and distracting at night. I can turn the dimming on and off manually, but it would be nice if it worked. I notice from a pinout of the car that the switch does indeed have a pin to the stereo, and the stereo has a pin to accept it. Did they just fail to hook it up? What do I tell them to get them to fix it? If they won't, can I do it myself? Thanks!

Thanks. I don't think I'll have Car Toys do things for me from now on... Car Toys Manager (Chad): "We'll do it for free if you want. We didn't connect it because it might blow a fuse." (??) Me: "I'll try it and see." Chad: "Actually, your stereo doesn't have a dimmer wire." Me: "Yes, it does. It's orange and white striped." Then he tried to sell me a $500 amp...