In the ground wire (ground wire or line 31) of the automobile circuit, the wiring method using the component and the metal part of the body (frame) as a common wire is called a single-wire system, and the part where the body and the electrical appliance are connected is called the ground iron or ground. The grounding points are distributed all over the body of the car. Due to the connection of different metals (such as iron, copper and aluminum, lead and iron), the electrode potential difference is formed. Some grounding parts are easily contaminated with muddy water, oil or rust, and some grounding parts are very Thin sheet metal parts may cause poor grounding, such as lights not working, instruments not working, horns not ringing, etc. Therefore, modern automobiles partially adopt a two-wire system, with special public grounding contacts, and draw a special grounding line diagram, which is comparable to the outline diagram of the fuse circuit. In order to reduce the line contact voltage drop during startup, ground wires with large cross-sectional areas are connected to the battery pole chuck, frame and engine body, and the contact parts are thoroughly derusted, depainted, and tightened.
The generator is connected in parallel with the battery, and the negative pole of the battery must be grounded. The positive pole of the battery is connected to the positive pole of the motor through the ammeter (or directly), the static electromotive force of the battery is usually 11.5V ~ 13.5V, and the output voltage of the generator is usually limited between 13.8V ~ 15V (24V electric system 28V ~ 30V). When the generator is working, the normal voltage is 0.3-3.5V higher than the battery voltage. This is mainly to overcome the line voltage drop, so that the battery can be fully charged without being overcharged.