How to Hardwire Into a Car Battery

Updated July 14, 2018

Occasionally, an electric device must be connected temporarily to an automobile battery. Typically, the device (such as a power inverter or jumper cables) connects to the battery using removable battery clamps. However, if the electrical connection to the battery must be permanent--such as adding an electric cooling fan to the electrical system--it may be necessary to hardwire the component to the battery terminal connection.

Cut a piece of electrical wire long enough to reach from the battery terminal to the electrical device. Strip 1/2 inch of insulation from each end of the wire.

Use a wrench to loosen the battery terminal retaining nut and remove the battery cable from the battery post. Cut the battery terminal off using the wire cutters and strip 1/2 inch of insulation from the battery cable end.

Twist together one end of the automotive electrical wire with the stripped end of the battery cable. Loosen the top bolts of the replacement battery terminal and insert the twisted wire pair into the gap created by the loosened battery terminal bolts. Tighten the bolts until the wire is snug inside the battery terminal then solder the wire to the terminal.

Attach the free end of the automotive wire to the terminal on the electric device to be hardwired. Solder the wire to the device terminal.


Do not hardwire both terminals on the electrical device directly to the battery as this will quickly drain the battery. Use an inline switch or relay to operate the hardwired device.

Things You'll Need

  • Replacement battery terminal
  • Wire cutters
  • Electrical pliers
  • Adjustable wrench
  • Automotive electrical wire
  • Soldering iron
  • Electronic solder
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About the Author

David Sandoval has served as a trainer and technical writer since 2000. He has written several articles online in the fields of home improvement, finance, electronics and science. Sandoval has an Associate of Applied Science in microelectronics from Northern New Mexico College.