Yeah, the Yel/Red power wire is key here and is protected by under-dash fuse #28.

 

so after all my multimeter research this is what I've come up with.

ground is good, accessory wire is good (hot - reading 12V) when I turn on the ignition. My only question is this... should the constant (white/blue) wire be reading 12V all the time (regardless of whether or not the ignition is turned on)? Because it's currently not.

 

Yes, the Wht/Blu wire should be hot at all times. This circuit is required to remember your preset radio stations. It also is required for the ECU to remember CEL trouble codes. Check whether fuse 47 (BACKUP) under the hood is blown. I don't think, however, that lack of power on this Wht/Blu wire circuit would prevent the radio from operating.

When the dash lights are ON, power is also provided to the Red/Blk wire to turn ON the radio light. This is controlled by fuse 30 under the dash.

Again, the Yel/Red wire is key for providing power to run the radio.

 

yes the factory colored white/blue wire (aftermarket solid yellow) should show +12V all the time. This wire has to have 12V for the radio to turn on. If it is not check in the fuse box under the hood for fuses number 41 & 47.

also the yellow/red is your ignition wire (aftermarket solid red)

edit: well it took me too long to type this so RonJ beat me to it

the Red/black wire is the illumination wire

 

Oh, I thought that power from the Wht/Blu wire is only needed to store radio stations (see below). If you are correct, then this must be the source of the problem.

 

One of the main uses of the +12V constant wire is maintaining all the station memory as well as all settings in the radio. but it also powers the unit and the built in amplifiers, and powers the relays that power the power antenna and remote outputs.

Every car stereo requires at least these 3 wires to be hooked up:

+12V constant to power the unit
+12V switched (ignition) only purpose is to tell the radio to turn on and off with the car
ground

every other wire is technically unnecessary but are usually needed for the radio to be fully functional. but it is possible to only use the 3 wires such as the case where someone runs all of their speakers off of separate amps via the RCA pre-outputs.

 

Thanks for the education.

 

no problem man. I work on car stereos for a living so I enjoy doing this stuff and helping anybody out when they need it

 

Thanks, I can tell. What is the function of the third critical wire that you didn't mention in your previous post? You described only two of the three.

 

oh sorry I put it in the previous post but now that I look at it again I realize it wasn't so clear.

1) +12V constant
2) +12V switched
3) ground

and technically the switched doesn't have to actually be switched. It just need some kind of +12V input, but hooking it into the accessory circuit of the vehicle is the only way to have it turn on and off on its own with the car.