First, I am not all that familiar with Gargraves track (I use Atlas).
However, I believe some folks use this type of quick connect and stick them in the slots in the bottom of the rails. These are just a couple of pics I found, one insulated and one non-insulated. You would need to get the proper size to fit the wire size you are using. Using the proper crimper is highly recommended if you are going to crimp as your only method of fastening. Many people using these connectors crimp and then solder the wires for best possible connections (crimper is not as important using this method).
Gargraves may even have some type of connector like this that they make for this purpose? I think they do have some type of stuff that slips in the bottom rail opening. Others that use the track can probably explain further.
The only other method I know of for that type of track is soldering directly to the track. This is the preferred method for some folks around here. Hope that helps you a little.
