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I am quite new at this so bear with my questions. I have purchased two 12 volt batteries which I will connect in series for 24 volt and to be used as house batteries. I drive a truck which has a 24 volt system. The truck's electrical system is grounded to the chassis on the negative terminal.

If I ground my house batteries to the chassis on the negative terminal, does it have any effect on the vehicle's electrical system? The starter on my car is 4 kW so I prefer to keep the systems isolated. I don't understand if grounding to the chassis can cause the house batteries to be pulled on when cranking.

The second question is, if I have grounded the house batteries to the chassis, can I drag one cable from the positive terminal on the house battery to a different location in the truck, and for negative simply use the chassis at that location?

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Perfectly acceptable to have the chassis as a common ground for both systems, and to use the chassis as a return for the house loads.

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  • \$\begingroup\$ Thank you. Bought a multimeter and was able to verify that common ground is positive on my truck. Grounded the new batteries on the positive terminal. Took one long cable from the negative terminal on the new batteries and verified with the multimeter that the voltage reading was the same between cable and chassis as between the terminals. All is well, thank you for helping. \$\endgroup\$ – Karl Oct 12 '18 at 7:56
  • \$\begingroup\$ Wow...positive ground systems are pretty rare these days. Just be careful with any 12V loads that may have the case grounded to the negative side - that's the usual case with audio equipment. \$\endgroup\$ – Phil G Oct 12 '18 at 13:47
  • \$\begingroup\$ Hi Phil. The truck I drive has a quirk. When the key is out, a magnetic switch disconnects ground (which is negative, read on). Plus however is always connected to the starter. Therefore, with key out of ignition there is current between the negative pole on the battery and the chassis. However, the car is grounded on negative. When the key is turned the magnetic switch activates and ground is connected again. This is why I thought it was ground on positive. As soon as I turned the ignition on, smoke billowed and the ground wire I attached burned up! Luckily, I and truck was unharmed. \$\endgroup\$ – Karl Oct 13 '18 at 16:21
  • \$\begingroup\$ I then consulted various sources and learned about the magnetic switch. Now everything is connected properly with ground on negative, and I have pretty much recovered from the shock! \$\endgroup\$ – Karl Oct 13 '18 at 16:22
  • \$\begingroup\$ That is definitely unusual - contactors or isolators are often fitted to prevent house loads from flattening the starting battery, but they are almost always on the positive side. A good reason why there should always be a fuse in every line from the battery apart from the starting circuit. \$\endgroup\$ – Phil G Oct 13 '18 at 18:23

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