Help installing a ceiling pendant light fixture
Was this a used fixture, because it doesn't sound like it would meet UL approval for new fixtures if there is no way to identify which wire should be connected to hot or to neutral.  Is there any ribbing or texture on one wire?  If so, that is likely the neutral.

I'm assuming your fixture just uses standard light bulbs.  From an electrical viewpoint of a standard incandescent bulb, it doesn't matter which way the current flows -- but it might matter for led or cfl bulbs (cfl = compact fluorescent).  However, from a SAFETY perspective, the polarity does matter (polarity is which contact on the light bulb socket is hot and which is neutral).  The uninsulated wire is the ground, which is always connected to the ground (bare wire) in the box.

I strongly recommend you identify which of the insulated wires (plastic covered) should be connected to the hot, and which to the neutral.  An easy way to do this is to take your volt/ohmmeter, touch one lead to one of the insulated wires and the other lead to the light bulb socket.  If you get zero resistance (the same as touching the two leads together) on the collar (side) of the socket, then that wire is the neutral (white).  If you get zero resistance when touching the button (bottom of the socket), then that is the hot.  Wrap a bit of black electrical tape around the hot wire.

Now you can install your fixture correctly, connecting the wires using the coding that you identified: white-white, black-black, bare wire-bare wire.  Use wire nuts to connect the wires.  The packaging on the wire nuts tell you what quantities of what size wires they are approved for use with.


Strip and straighten 1/2" to 5/8" of each wire to be joined.
Hold the wires together, straight and parallel.
Put a wire nut over the wires, covering all the stripped wire, and twist clockwise. Turn until the wires outside the connector start to twist.
Test the connection by holding the wire nut with one hand and tug on each of the wires with the other hand.  The wires should be firmly connected and not slip out of the wire nut.


Forgot to add: it's unlikely this is aluminum wiring.  Could it be stranded wire that is soldered on the end?  If it is aluminum wire, then you need to use fasteners approved for use with aluminum.