I just bought my first 350z (2005 350z with 115k touring edition). However, it has a very odd sequence of problems that somehow seem to be linked together.
1. First I noticed the triple meter stop working (orange light come on but not gauge readings). --> From that and the FSM I attempted putting the dash in Self-diagnostic mode (the speedo and rpm worked) but the triple meter showed nothing.
2. The car has a full tomei exhaust from the cat back and a z1 plenum spacer.
3. A day or so later I noticed the passenger side tail light was out. --> I replaced both sides with new LED bulbs and turned the car on to make sure they worked.
4. When turning the car on the SEL came on and somehow the triple meter started working again.
5. Ran codes and it threw a P0300 and P0444 ---> Just for kicks I canceled them both and repeatedly turned the car on and back off.
6. After doing that the P0300 went away but the P0444 came back and then after driving around P0300 came back again.

FYI:
I wired up a double din head unit to the dash as for some reason the buyer had removed all the stock sound system. So I wonder if he may have done something when removing the audio system.
I have read lots of forums and look at the service manual.

Could the P0444 be causing the P0300 (I read in one guy's case that seemed to happen) not totally sure again though

Any input is appreciated.

 

Very possible if you have a vacuum leak to have both issues. Make sure evap line is connected to the intake manifold. Would also check all other lines including to the power booster under the cover if you don't see anything cracked or disconnected.

 

On the other issue, did installing the new radio fix your gauge issue?

 

First I did a temporary wire to the head unit and the gauge did not work, then I went make tighten all the solder joint and what not and installed the tail light bulbs and bam the gauges work, but I am interested to see if they go out again.