2003 chevy s10 installed my aftermarket HU correctly a few weeks prior. out of no where the 12v switched get constant power no clue why. Worked fine before today and I didn't even mess with it. Any reason as to why my previously switched 12v wire has changed to constant? Both constant and switched read 12v on multimeter after truck is off and keys are out. Any help is much appreciated please and thank you.

1 Answer 1


Suggest you pull the fuse that supplies the head unit, then check for 12V on a switched circuit such as your ignition.

If the ignition no longer has 12V, either you made a wiring error when installing the HU or the HU is either defective or it includes a design defect. (Even money says it's your wiring error -- no offense!)

On the other hand, if switched circuits still have power, the only obvious reason would be a broken ignition switch. That's easy to check with a meter but not so easy to access.

If your ignition is consuming power 24/7, better be wary of running the battery down to the point that it won't start.

  • Most cars supply accessory power to radio until the key is off and the door is opened. I don't know if that applies to a 2003. But worth checking out.
    – Jupiter
    Commented May 26 at 21:15
  • Thank you didn't expect anyone to be on it this quick Commented May 29 at 2:06
  • I pulled the fuse and checked and it had no power but what I mean is when I installed it previously the dark green wire was only getting power when the key was on. It is now getting power when key is off and out of ignition when it never did that before. The wire itself changed from only being on when the key was on to being constantly. Commented May 29 at 2:18
  • @CharlesMjelde The words "ignition wire" in the title of your question were assumed to mean "the wire that powers the ignition", i.e., ECU, coil(s), crank sensor, etc. That's not what you mean. So the second paragraph of my answer applies if you replace my word "ignition" with "dark green wire". The HU is providing full time power to it, and it might be powering other accessories. To confirm, disconnect dark green from HU. If it no longer has power with ignition off, it's confirmed.
    – MTA
    Commented May 29 at 11:59

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