Now I know this is a "Ford Forum", but here are pics of me installing my wife's HD Radio (her Christmas present), into her 1995 Oldsmobile Silhouette.
Taking the dash off...
Taking the factory deck out...
The HD deck...
The pre-existing antenna was too small so I had to make my own...
Things are coming together...
Putting it all back together...
Dash back together...
Now to hide the box and wires...
All done!
How this HD radio works: it takes the existing antenna wire as input then it runs an antenna to the stock radio from the HD deck. It also requires three wires: constant hot, switched hot, & ground.