How to Connect 12 Volt Auto Lights to AC

Auto lights are designed to operate on 12 volts DC (direct current) but can also operate on AC (alternating current). The trick is maintaining the voltage at 12 volts to keep from blowing out the bulb. Because the most common voltage of AC found is 120 volts, the voltage must be either lowered, or multiple lights must be placed in series to reduce the voltage across each light. If the the voltage remains at 120 volts after it is converted to DC, it would take 10 DC light bulbs wired in series to handle the voltage without blowing them out.

• 1

  Connect the two wires on the power cord to the two terminals on the primary side of the transformer. This is also called the 120-volt side. Each wire should connect to one of the two terminals. This supplies power to the transformer.

• 2

  Place 12-volt auto light bulbs into each of the three light bulb holders. Cut six 12-inch pieces of electrical wire and strip 1/2 of an inch of insulation off of the ends of each wire. Label each light bulb holder L1, L2 and L3.

• 3

  Connect terminal 1 of L1 to terminal 1 of L2. Then connect terminal 1 of L2 to terminal 1 of L3. Connect terminal 2 of L1 to terminal 2 of L2. Then connect terminal 2 of L2 to terminal 2 of L3. This connects all of the lights in parallel so that each light will get 12 volts.

• 4

  Connect terminal 1 of L1 to one of the two 12-volt terminals on the secondary side of the transformer. Then connect terminal 2 of L1 to the other 12-volt terminal of the transformer. Plug in the transformer and observe the lights. The lights should all be on.