I’m in the process of trying to replace my head unit with an aftermarket double din. I’ve been heavily utilizing Wrathernaut’s guide. I have my head unit wired to a PAC ROEM-NIS2 wiring harness, which is then plugged into the harness for the factory Bose amp. The head unit does not turn on when the key is turned to the accessory position. I finally gave up after triple-checking everything and took it to my local Car Toys. The rep there was awesome, and hooked the head unit up to an independent power source to confirm it would turn on. He then took a multimeter out to my car to test the voltage of all the connections. When the car was on, there were only 2 volts coming from the factory harness. He finally admitted that he had absolutely no idea what could be going on. So I’m turning to you guys. What the hell is going on? The stock stereo worked completely fine before I started this install and as far as I can tell, no fuses are blown. I’m confused and frustrated...

The Yellow wire should have power at all times.
The Light Green wire should have power only when the key is turned on.

Grab a multimeter....check it out. Are you grounding to the frame?

I’ll get some pics this evening. Bad ground is the only thing I can think of, but in that case, why would the factory stereo work?

Rep at Car Toys checked every connection. Only 2v at every point.

I dont trust "professionals" too much. Ive seen a lot of mechanics and installers not know what the hell theyre doing.

Just be sure and check it yourself so we can help figure out the next step.

The factory harness is plugged into the PAC harness using the original connector, which is then crimped to the head unit. We already confirmed that the head unit is functional and the crimp connections are good.

He checked it right in front of me with a multimeter. ~1.9v on both the constant and switched power wires across the entire setup.

Just found an old post saying the power mirror fuse has an effect on the stereo as well.

Strange...but a quick check wouldnt hurt.

Fuse seems to be fine. My power mirrors work

Here are some pictures of the entire setup. Hoping it’s something easy that I screwed up on my end at this point. A little embarrassment is better than a bill from a shop.

Was your mechanic checking voltage at the factory harness, before it connects to the PAC?

yes, he tested both.

Issue still isn’t resolved. I’ll make one more pass of any fuses I can possibly think of just to double check, but at this point I’m at a complete loss as to what it could be. Seems like everyone else has had success with this exact setup with no issues.