Pioneer 4100NEX install issues
 

Hey guys, first post here and I'm having some issues with installing my 4100NEX. I have the PAC wire harness all wired up to the head unit, as well as the parking break and ground wires grounded, and I have the AC hookup plugged in. The only thing I have left to do is hook up the steering controls, so I decided to test the radio by turning the car on. Whenever I turn the car on though, the radio doesn't turn on, however the buttons on the face of the radio continuously flash blue. I have no idea what the issue is and would greatly appreciate help!

Aftermarket radio's require 3 wires to turn on. Yellow for constant, Red for ignition (which also triggers it to turn on) and Black for ground. Do a bench test by twisting the yellow and red together and connect to +, black to - . After you verify it does indeed work, retrace the wires going into the car. Chances are you might have accidentally mixed a couple.
As far as the buttons flashing, if it's anything like my last 2 Alpine units, the dimmer is set too low. Also try running a wire from the battery - terminal straight to the H.U when it's plugged into the harness just to test if it needs a better ground. When I did my dual tablet install, the ground wire on my adapter did not work at all. The OEM radio was chassis grounded, so I have no idea if my 04 even had a proper ground cable. I ran my own from the battery.

If the radio's not in the harness and the harness attached to the chassis, you don't have a ground - unless you've attached a separate grounding wire to the chassis yourself.