What are the four wires of the fuel pump relay?
3 Answers
Automotive fuel pump relay wiring configuration: The four wires of a car fuel pump are as follows: 1. Two wires belong to the fuel level sensor (commonly called the float) - one is the power supply wire, and the other connects to the fuel gauge; 2. The remaining two wires are for the fuel pump itself - one is the power supply wire, and the other is the ground wire. The fuel pump operates with high current, hence its wires are thicker, while the sensor wires are thinner. Additional information: Automotive relay function: It serves as an "automatic switch" that uses small current to control high-current operations. In circuits, it performs roles such as automatic regulation, safety protection, circuit conversion, and switching. If a car relay fails, the simplest consequence is that certain functions may become inoperable.
I recently had an issue with the fuel pump relay during a car repair, and those four wires really can't be connected randomly. Generally, two are control wires: one called terminal 85 connects to the ECU's control signal wire, and the other, terminal 86, is the ground wire. When the car starts and the signal comes, the relay engages. The other two wires are for the main circuit: terminal 30 is the input wire directly from the battery positive, and terminal 87 is the output power wire to the fuel pump. If you DIY a relay replacement and mess up the wiring sequence, the fuel pump might not work or the relay could burn out—I once replaced it and the car wouldn't start, only to find out after much hassle that the terminal 86 ground wasn't properly connected. I suggest checking the manual or asking an experienced person for help before repairing. Wiring is all about small details causing big troubles, especially when it involves fuel system safety. Remember, don't mix up the positions of the main power terminals 30 and 87. The control terminals 85 and 86 can be swapped to some extent, but it's not recommended to tamper with them casually.
The four wires of the fuel pump relay are divided into the control group and the power group. In the control group, pin 85 is typically connected to the signal output line of the electronic control unit, and pin 86 is the ground wire, which are responsible for triggering the relay closure with low current. In the power group, pin 30 is the input line from the battery positive terminal, and pin 87 supplies high-current power to the fuel pump motor. This design ensures that the fuel pump is only powered when the engine is running, protecting the system. If you attempt to repair it yourself, be careful not to reverse the positions of pins 30 and 87, as this could cause a short circuit, or mix up pins 85 and 86, which could send incorrect signals and prevent the fuel pump from operating, affecting driving safety. A multimeter can be used to check for continuity and confirm if there is a wiring fault, but due to the high voltage and risk of sparks, it is best to leave it to a professional mechanic. In simple terms, distinguishing between control wires and main power wires helps avoid accidental risks.
