Good to hear that you got the starting problem fixed Stott ...
WRT voltage fluctuations ... You need to install independent supplies to
the stereo and the gauges. That fluctuation that you see in the gauges is
also causing distortion in the sound you hear. I usually run a heavy gauge
wire directly from the battery to the stereo ... that should fix all of your
problems. Make sure that you install an in-line fuse near the battery,
things could get nasty if the insulation got rubbed off otherwise. On the
TQC it wasn't too tough to snake a power wire under the carpet when I had
the seats out. On the Fox it was as simple as running the wire through an
existing loom through the firewall.