Ah yes the pesky parking brake signal. I ran into this on my ILX-107 Install. After some research I found that the magic formula is that the HU starts up, then expects this signal line to be pulled low (Grounded) to allow the user full functionality. Sometimes it even wants Ground-notGround-Ground. If it starts up already being low, and staying low, it will not trip...that's Alpine's attempt at being clever to keep you from just tying this to a ground lug.
Sounds like you got the answer you were looking for, but if you eventually get annoyed with getting locked out of your settings and some functionality while driving consider the following:
Bottom line is you have to have some way to ground this ~30sec after the unit turns on. I ended up making a really inexpensive sensor that engages with the parking brake in the opposite way as originally intended. Drop the e-brake and you can use everything.
Some people will use a toggle switch instead which works fine but you have to find somewhere to put it. I'm not the biggest fan of making holes with no going back.
https://www.digikey.com/products/en/...T&pageSize=500
I've seen mentions of the bypass modules and can not attest to their effectivity...but at the end of the day you're paying considerably more than the above 2 solutions for the same effect...and reliant on whatever is in the module to not wear out.
https://www.amazon.com/MicroBypass-P.../dp/B006FKAHFM