I just installed a new head unit (a cheap ML41B) and realize now that it's not getting constant power (time/presets are lost when the car is turned off). I noticed the yellow line from the vehicle doesn't have a matching connector on the head unit, so I assume I need to re-wire something, but I'm just not sure exactly what to do! Pics below (including the manual). Appreciate any advice!

head unit wire harness 1 wire harness 2 manual

1 Answer 1


My main thinking is you need to exchange the Power B+ with the ACC +. You aren't getting a constant power to your head unit which you need to save your presets. The most common thing to go on here is you've got these two wires backwards.

Something you might check before you go swapping wires, is just to check your fuses. You may have inadvertently popped the one for the constant.

  • Ah interesting. Wouldn't I just want to switch Yellow with Brown/Red on the cable coming from the vehicle? That would put Yellow on Power B+. My concern otherwise is having to manually power off the radio when not in use.
    – Rob Lauer
    Apr 9, 2023 at 15:55
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    @RobLauer - I don't know which colors are on the car, I'm only suggesting swapping the two leads as it shows in the diagram. You can test these two leads with a multimeter to see if my "thinking" is correct. One of the two leads will have power all the time. This should be connected to Power B+, which is an always on source. It provides the minimal amount of power needed to keep your settings. The other one is the switched power with the ignition which is the main power, provided for when you're actually using the head unit. Apr 9, 2023 at 16:13
  • Good call on the multimeter - turns out the line that should be providing constant power from the vehicle is only provider power when the vehicle is on. Not sure where to go next but at least I have something else to figure out - I appreciate the help getting here!
    – Rob Lauer
    Apr 9, 2023 at 21:49
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    @RobLauer - If worse comes to worse and you can't figure it ou, just run a second line off a constant source. Apr 10, 2023 at 0:16

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