Which is the constant power, ACC or VCC?

[KennedyMarie]

VCC is the constant power wire. Relevant introductions are as follows: 1. VCC wire: Test method using a 12V car bulb - Generally, the black wire is the negative pole. Connect one end of the bulb to the black wire. If the other end is connected to the VCC wire (the bulb stays constantly lit without key control), it's the VCC wire; if the other end is connected to the ACC wire (the bulb turns on/off with key control), it's the ACC wire. 2. ACC wire: Trace along the ACC switch path. You can use one end of a test pen to touch metal and the pointed end to probe the ignition wires under the steering wheel. First turn on the left turn signal, then when probing the correct wire, the small light on the test pen will flash synchronously.

[LolaDella]

Having worked in automotive circuits for so many years, ACC is the accessory power, which only gets electricity when you turn the key to the ACC position, like when you turn on the radio. Constant power, often referred to as VCC in some circuit systems, means it's always live and usually directly connected to the battery's positive terminal. So, VCC is constant power, while ACC is not. If you connect to the wrong one—say, hooking up an anti-theft device to ACC—it might trigger a false alarm when the car is turned off. But if you connect it to VCC, it could drain the battery by constantly drawing power. Once, I helped a neighbor trace a power drain, and it turned out their dash cam was mistakenly connected to VCC, causing the battery to die the next day. This distinction is crucial—always use a multimeter to check voltage before installing any device to avoid issues.

[OVivian]

Last time I modified my car audio system, I messed around with this: ACC is accessory power, which only activates when the key is turned to the middle position, like the cigarette lighter. VCC on the wiring diagram is the constant hot wire, meaning the battery's main power line that never turns off. So VCC is the true constant power, while ACC is just a temporary power source. Not understanding the difference can lead to serious trouble—for example, if you install a USB charging port on VCC, it will keep draining power even when the car is off, and the battery could be dead in just two nights. I made this mistake myself, and only after learning more did I realize that a circuit tester can easily confirm the power supply type.

[LeMarley]

As an ordinary person who drives daily, I have to say that ACC refers to the circuit that's only powered in the ACC ignition state, like the radio for listening to music. VCC mostly refers to direct battery power, which is the constant hot wire that supplies power even when the engine is off. So VCC is constant power, while ACC is not. This distinction is very practical - if the car lights are connected to ACC, they'll turn off when the engine is stopped, but if connected to VCC, they might cause battery drain and affect next-day startup. For safety, I always check the vehicle manual or simply use a circuit tester to check the wiring to prevent potential hazards.

[GiselleFitz]

In my small electronic projects involving automotive circuits, I learned that ACC stands for Accessory Control, where current flows only when the key is in the ACC position; VCC, on the other hand, is the voltage supply source, typically a direct battery connection, maintaining constant power. VCC is indeed the constant power source. Distinguishing between these is crucial in DIY designs. For instance, connecting a sensor to ACC means it will turn on/off with the car, while connecting it to VCC might lead to battery drain and reduced lifespan. You can easily verify the power supply differences using a multimeter in daily use.

[VonWalter]

When tinkering with car repair parts, I learned: ACC is the accessory switch power, which only works when the key is in the ACC position, such as when the fan starts. VCC on most cars represents the main battery supply line, which is a constant hot type. So VCC is the constant hot wire. Misconnection can lead to major issues, such as a GPS antenna connected to VCC draining the battery even when parked. After experiencing this, I realized the importance of using a test light to measure first to avoid risks.