A double din unit will fit in the Trailblazer/Envoy platform vehicle however you will need adapters. If you are experimenting then you are best to let a pro do it.
Look under the driver side dash, near the front. You will see the plug there.
Under the dash
If your Trailblazer is a 4x4 the switch should be to the left of the radio on the dash.
It is under the dash on the driver side.
The OBDII connection is under the driver side lower dash panel around the steering column area.
show me how the symbols look for a 2007 Chevy trailblazer
it's under the hood
It has 1 in under the dash. passenger side.
On the driver side of the dash and under the hood on the driver side.
The drain for the condenser may be clogged.
Sounds like you need a new battery.
The symbol of a wrench and an oil can on the dash of a Chevy Trailblazer means that your vehicle needs oil. If the light doesn't go away oil is added, you need to take your vehicle in for service.