The purpose of the negative terminal on a car battery is to provide an electrical connection for starting, lighting, and ignition systems in your vehicle. A ground wire provides grounding for electric circuits. So what we need here are two separate wires: one as our ground and another as our power supply (negative).
Unless the car is a hybrid, in most cars, both batteries are grounded by a common negative cable that connects to the engine block. In these vehicles, you can use either battery as your ground depending on which side is closer to potential grounding points in your vehicle's body, for example, an exposed bolt head or structural steel. For non-hybrid cars (which almost all older models aren't), you may want to make sure the battery terminal and ground cable do not short if they structurally touch metal or other grounded parts of the engine block; we recommend using at least six inches of electrical tape wrapped around them to get their voltage difference away from metal and each other (and if desired, clamping them with a bolt, as long as it's snug and insulated from touching your car with anything metal).
Is the negative terminal on a car battery grounded?
This is a common question that comes up when you're looking to ground something in your car. While the negative terminal on your battery might look like it should be grounded, most batteries are "negative ground" systems which means they cannot be used as grounds.
The negative battery terminal isn't grounded because it is attached directly to the car's chassis. Many cars have an electrical system that uses negative ground, and grounding would cause a short circuit, making the situation even more dangerous than just having ungrounded electronics.
Some exceptions do exist, though: older vehicles with positive ground systems might still use the negative lead on the battery. An additional negative connection to chassis isn't possible in these cases because of how they are designed, but it can be used as an alternative ground in certain situations.
There is one other situation where you might use a car's negative terminal for grounding: when there is no better option available and none expected anytime soon (if ever).
For example, when you want to use a car battery as an auxiliary power supply in the back of a truck or van. Since there is no better ground available (e.g., batteries for starting and auxiliary electronics are usually not connected), it might be ok to do this once in a while; but don't make this standard practice.
In general, if you're not sure whether it's ok to use a terminal as ground or not - don't do it.
One last thing to keep in mind is that always disconnect the negative terminal whenever you are working on car electronics or want to test something with them. Disconnecting it protects the battery from unnecessary wear even if everything seems fine at first glance.
This can save you a lot of money over time and makes sure your new electronic gadgets are safe to use with your car.
Can you connect ground wire to battery?
In general, it would be wise to not connect the ground wire from one battery to the other in a series circuit because doing so will put both batteries at risk of discharging over their voltage range. This is especially true when connecting the ground wires from different types of batteries or brands, resulting in very different characteristics in current and discharge rates.
But should remember that this may reduce the lifespan of your car's electrical system. The negative terminal is connected directly with body parts like chassis and engine block where metal part are already grounded. You will lose out on free electrons during the charging process since it would be shorting itself through grounding rather than successfully transferring electrons to the battery.
It also wouldn't be safe because all of the metal in the car would carry electricity trying to escape from the main connector; it would cause a short circuit and could start sparks, an arc, or even an explosion more easily than any other resistance (because there's nothing for it do but build up like crazy).
A negative battery terminal as the ground is not advisable. There are better options available for you to use if your car needs it. If there's an issue with the positive cable, then that would be where you need to attach the grounding wire. You can also have issues with corroded or broken grounds on your alternator and regulator, so you need to identify the problem before you attach any grounding cables.
For more information on grounding your vehicle, talk with a mechanic or auto dealer who can help get your car running correctly again. If you have questions about what is wrong with your battery or alternator, take it into an automotive shop for inspection and testing. This way, they are aware of the issue and are more likely to be able to tell you what is wrong with your car.