Hot Rods Wiring for dummies question

Bought a dome light that has three wires. Hot, ground and zero. What is the zero line and where do I connect it? Thanks.

 

I think one is to the light, one is to the switch and one is the local ground. Depending on the colors of the wire. If two are the same color they are for the switch and the ground and the other would be hot.

 

Still confused. Here's a little diagram. Two pole switch. One pole to 12v, other pole to red wire on light.
Black wire goes to ground. Where does yellow wire go? Thanks for the help.

 

maybe one wire goes to the headlight switch to turn the dome light on. One goes to the door switch to turn the dome light on when the door is opened. And one wire to a ground. This is just a guess.

 

Ok, thanks. I'm not using the headlight or door switch, so I guess I can just use the red and black.

 

If the light has a built-in on-off switch, one 'hot' will be for connection to an external switch (door, main light switch), the other 'hot' will be direct 12V power to the internal switch. The ground is a ground. Use the one that goes to the switch, and make sure you insulate the unused other as it will become hot when the light is on.

 

Ok, thanks. That clears it up for me. Appreciate everyone's help.

 

Dome lights work differently from everything else. Normally, electrical things are grounded - headlights, wipers, radio, etc. To make them work a switch provides 12V to them. Dome lights are the opposite. They always have 12V wired to them. To operate a dome light a switch has to provide a ground to the light. Door switches have only one wire. When you open the door, the switch grounds that wire and that causes the dome light to go on. So on a dome light, the ground is switched. On everything else the 12V is switched. Now... Your three wires are probably: 1.) permanent 12 V to light, 2.) wire from door switch that will supply a ground to light when door opens, and 3.) a wire that needs to be permanently grounded so that switch on dome light will work. If you are not using door switches you'll only need two wires - the permanent 12V and the permanent ground.
Here's my guess on where each of your wires go:
Your "HOT" is surely for the permanent 12V. Your permanent ground is probably "GROUND". "ZERO" must be for door switches.