Audio Systems: 96 GMC Jimmy radio on/off in hot weather, electronic thermometer, gmc jimmy

Question
I moved from the Northeast to Texas last year and have notioced this year that on a really hot day with high humidity (95°, 85% humidity) my factory installed radio/CD player in my 1996 GMC Jimmy will not come on.  There is no display.  In fact, the overhead electronic thermometer and compass also do not come on.  Once the outside temperature cools down in the evening, the radio and compass come back on and in fact all of my preset stations are still there and the time is still correct- indicating that the radio never lost complete power.  What would cause this and how do I prevent it?  LAst summer was much hotter than it is now and I did not have this problem before now.  Thanks.

Answer
both of the systems have 2 powers
cnstant power always on keeps all the memory stations and temperature settings
the power comes from the ignition this power turn on both devices  
the radio turns off when the temperature is over 105°

check the ignition ouput