Ignition/ACC low voltage?

[JoeWood]

I'm trying to put in a new head unit on a 2007 Chevy Silverado 1500 Classic, and for some reason, I'm only getting about 4.5v when car is started. The fuse seems fine, not sure where to look next.
Anybody have something like this before?

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[1aespinoza 10+ year member]

Anybody have something like this before?

Is this on both power wires? The constant and the accessory.

 

[JoeWood]

Is this on both power wires? The constant and the accessory.

No, the Constant is 12v. the accessory is low, so low that it doesn't actually trigger the head unit.
If I bridge the constant to the accessory, everything works. Just the Accessory isn't working correctly.
I thought I had got a reading of 4 volts, but now every time I try I'm only getting like 0.5v.

 

[1aespinoza 10+ year member]

Just the Accessory isn't working correctly.
I thought I had got a reading of 4 volts, but now every time I try I'm only getting like 0.5v

May be the accessory relay.

 

[audiobaun 5,000+ posts]

Did you get the correct wiring harness for the HU? If not.. Its possible the pin connection isnt making full contact in that slot

 

[JoeWood]

Did you get the correct wiring harness for the HU? If not.. Its possible the pin connection isnt making full contact in that slot

I did yeah. The OEM Harness was frustrating because the pinouts for the aftermarkets had the wrong layout. I have it correct. I'm measuring low voltage out of the acc wire probing at the OEM harness. Same issue with the OEM radio.