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Easy question (or at least I think). I've installed a siren in my vehicle which calls to pull power direct from the 12 volt battery. I currently have the circuit completed by connecting to the negative terminal on the battery. I've been told that sometimes it is best to connect to a grounding point on the vehicle like the frame.
Is this necessary for my situation or ever?
Thanks in advanced!
The negative of the battery is connected to the chassis so run your postive to the battery (make sure it is fused) and connect the negative of your siren to the chassis. Look for any bolt nearby, use a ring terminal and fix it down. However do make sure that the chassis surface is bare metal (sand it down), any significant amount of paint will result in a bad connection and cause problems.
You should avoid connecting cables directly to your battery. There's no point at all. The negative terminal of the battery is connected to your car body, so you can connect your siren's negative terminal directly to your closest ground point (car metal body). There's no reason to have multiple cables on your battery's terminal. Cable harness will be more organised.
In a car the amount of iron (even though not as conductive as copper) is so substantial that a short wire to the nearest chassis point is the best (lowest resistance) ground for an accessory in almost all cases.
Running a wire to the battery minus is also fine for low current loads as well.
High current and long earth wire can cause earth potential issues but these seldom matter unless there is a further connection to some other device at the end of the long power cables.
