How to connect spotlights to a relay

Written by richard asmus
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How to connect spotlights to a relay
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Since automotive spotlights carry relatively high current, you should wire them through a relay to protect the contacts of the switch that turns them on. Since the types of spotlights and relays vary, you will need to select tools, terminals and wire according to the manufacturer's specifications. You also need to find appropriate points in your vehicle to connect to the battery and ground. You should protect the wire you connect from your battery with a fuse--either by using one already installed in the vehicle or by using an in-line fuse that you install on the wire itself.

Skill level:
Moderate

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Things you need

  • Basic electrical tools
  • Wire
  • Connectors
  • Wiring diagram of your relay
  • In-line fuse (optional)

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Instructions

  1. 1

    Connect a wire from your battery through a fuse to one terminal of the coil of your relay. Use a fuse with an amperage rating high enough to run all the spotlights you will run with the relay and the coil of the relay itself.

  2. 2

    Connect the other side of the coil of the relay to one side of the switch that will operate the spotlights. Connect the other side of the switch to chassis ground.

  3. 3

    Connect a wire from the battery connection to the coil of the relay to the common (C) connection of the relay. This is the armature that will move to the output contact when the relay operates.

  4. 4

    Connect a wire from the normally open (NO) terminal of the relay to each of the spotlights. Voltage from the battery appears on this terminal.

Tips and warnings

  • You can run one or more spotlights with this relay. Use a fuse and relay with an amperage rating high enough to carry the current of all of them.
  • See page 3 of the autoshop101.com reference for a wiring diagram. Substitute "spotlight" for "horn." The principle is exactly the same.
  • See the reference at reuk.co.uk for a wiring diagram of a standard Bosch automotive relay, a most likely choice.
  • For more than one spotlight, you can run a wire continuously from one to another. You don't need to run a wire from each spotlight to the relay.

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