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I am planning on hooking up a 4-pin relay to supply power to ignition coils on a motorcycle.

The on/off switch on the diagram below is the ignition switch operated by the key. Ignore the fact that pin 87 and 30 do not lead to anything; I left that out to keep the diagram simple. I also did left out a fuse to keep the diagram simple.

relay wiring diagram

When the switch is turned ON, will I be shorting the battery? How is using a relay in this case different than connecting a wire between the battery + and - poles?

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No, you will not be shorting the battery. The relay COIL, for a 12V relay, is designed so that when it's energized (i.e. connected between 12V and ground) will only pass enough current to close the relay contacts.

Technically, the relay coil is generally a wire winding around a core material, usually laminated iron pieces. The coil presents both an inductive load and a resistive load to the battery. In the steady-state condition, where the 12V has been applied for a while, the coil behaves like a resistor and will not short-circuit your battery. If you check the specs for the relay, usually the typical current drawn by the coil will be listed.

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  • The current drawn by the relay coil is usually measured in milliamps for small relays. Larger ones can take higher currents.
    – Solar Mike
    Jan 12, 2020 at 0:22

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