Tom, I know you asked this question of our " Hyundai Hero " but I had the
same problem a couple years ago. Start by pulling the radio back out again
and make sure its WIRED CORRECTLY !! Some radios have a wire especially for
the light in the radio and it may not be hooked up right, and while its out
you can check the rest of the wires and make sure thier all taped correctly
and none are bare or touching what thier not supposed to be.  I would do
this before you wasted anymore fuses. Also make sure the power wire and the
ground wire are where they should be.

Tunez

I'm not Hyundaitech, but I'll give it a try.  At least on my 01 Elantra
there was a wire in the harness going to the radio that went to +12V
when the dash lights were on.  Offhand I don't know which color code
wire it is, but www.hmaservice.com may have it, or hopefully your son
who installed it should have the information.
Anyway, I would start with a visual inspection of the wiring behind the
new radio, focusing specifically on that wire.  If there are no visible
problems, I'd disconnect the whole radio at the harness and see if the
lights work again.  I'm presuming they will, since this all started
when the radio was installed.

Lastly I would disconnect this dash illumination wire and make sure the
problem has gone away (and make sure all the functions of the radio
still work) to confirm that we are looking at the right wire.  If when
the wire is disconnected the dash lights and radio work normally, you
either have a short somehow in that circuit (which you should have
found before) or it's possibly just not connected to the right wire on
the radio.  Either way it should be well narrowed down by now.

Good luck.
Ben

Tunez and Dreyfuss are right on track here.  There are two wires going to
the radio for the illumination circuit.  Most aftermarket radios don't use
these-- they keep illumination on anytime the radio receives ignition
power.  Make sure they aren't for some reason hooked up to the aftermarket
radio, and make sure there are no bare ends that can touch things behind
the dash.  If you unplug the radio to recheck, remember that you'll need
to reconnect the rheostat found on the left side of the dash facia you've
removed to get to the radio.

Unless you have a TDR instrument, the only way I know of is to trace the
circuit starting and one end and working towards the other.  Did the
problem start shortly after the radio was installed?  It so, then a good
chance that these events are related.  I'd pull the radio and look for a
wire that was pinched when the radio was installed.

Matt

Thanx for all the fast replies.  Did I mention that everything in the radio
works just fine??

I will still look for that supposedly "extra" wire.

Thanx again!

Tom Wenndt