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I'm trying to set up an electronic device to operate inside a vehicle. Power should be 12v 1 amp fuse. I was going to use a cigarette lighter for power, but the instructions say to ground one of the three wires. We have a portable inverter in the truck that is hard-wired to the trucks fuse panel. Can I get around the need to run a separate ground by using a grounded plug into the inverter? Or how dumb is that?

Thanks

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It's an "Azimuth R1000" autocompass. Typically used for boats, but we are using it in a truck as part of a wildlife telemetry project. Three wires are white, red, black. Red goes to power, black to ships ground, white to a toggle switch, then back to power, per the instructions. It's definitely designed to be permanently installed, but I can't do that in this case. I also have a cigarette lighter adapter (with leads pre installed) I was going to connect to draw power

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Just connect it to the car's chassis. In automobiles, the common GND is always the metal body of the car. Source: https://en.wikipedia.org/wiki/Chassis_ground

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The meaning of the term "ground" depends on the context. With DC, it can often just mean the "negative" 0V node. Most vehicles nowadays have the entire frame/chassis of the vehicle connected to the negative terminal of the 12V battery. With AC, ground often refers to the literal Earth. In the case of a mobile inverter, there is no Earth, but that's outside the scope of this.

The cigarette lighter socket itself will have a positive and negative. The standard in North America is for the frame (ring) of the lighter socket to be negative (ground), and the center (tip) will be positive.

You didn't mention what device you're trying to power, nor what the 3 wires are, so it is difficult to say with certainty how to wire your device.

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  • \$\begingroup\$ Thanks ! Sorry, I didn't want to get too in the weeds. It's an "Azimuth R1000" autocompass. Typically used for boats, but we are using it in a truck as part of a wildlife telemetry project. Three wires are white, red, black. Red goes to power, black to ships ground, white to a toggle switch, then back to power, per the instructions. It's definitely designed to be permanently installed, but I can't do that in this case. I also have a cigarette lighter adapter (with leads pre installed) I was going to connect to draw power \$\endgroup\$
    – tlyons253
    Jul 6, 2023 at 13:59
  • \$\begingroup\$ FYI - Some vehicles have cigarette lighter sockets with positive nodes that are connected and disconnected automatically depending on either the key position or the engine status. (The negative ring will always connected to ground). If your compass needs constant power on the red wire (to retain memory for example) then you will want to test the specific lighter socket you're going to use. You may need to connect the red white more directly to the positive bus bar. \$\endgroup\$
    – Bort
    Jul 6, 2023 at 14:07
  • \$\begingroup\$ Thanks! Constant power is not needed. \$\endgroup\$
    – tlyons253
    Jul 6, 2023 at 14:14
  • \$\begingroup\$ In 99.9% of automotive electrics, "ground" just means the vehicle's chassis, which is in turn connected to the negative terminal on the battery. The device you're powering needs two power supply connections - red wire to positive, black wire to negative. \$\endgroup\$
    – brhans
    Jul 6, 2023 at 14:29

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