[Yaesu] VX-5R Question

[Ted Sarah - W8TTS]

I'm going to be using my VX-5R for APRS from time to time, and have
run into a minor problem.  When I hook it up in the car using the
E-DC-5B DC Cable, the keypad/LCD illumination comes on, as well as the
  green TX/Busy light.  When I transmit the lights go off, until a
signal is received and then they come back on.  I have the following
options set as indicated:

   01-Squelch Level = 6
   13-Scan Lamp = Off
   17-Busy LED = On
   25-Lamp Mode = Toggle

I've tried adjusting the Squelch Level to no avail.

Also, when running on the DC Cable, it shows the APRS interface device
(Tiny Tracker 3) a solid receive signal, unless the volume is turned
way down.  When running on batteries, the radio works as it should.

Any ideas?

-- 
73 - Ted - W8TTS