Just bought a double din Pioneer stereo to go into my 2003 Octavia elegance, all fitted fine until I tried to turn it on, got no  power going to it  , checked the fuses, checked the voltage on the standard ISO, and found on pin 4, the voltage doesn't come up to 12v when the ignition is turned on. The standard radio works fine, but does have to be turned on and off manually, but I tried turning on the double din stereo, and another aftermarket pioneer stereo with no result.

 

 

Are there any other clues or steps that I may have missed out as I know it is a slight issue with some models?

You'll probably find the info you need in the ICE forum. There's a sticky regarding ISO which may help you. 

http://www.briskoda.net/forums/forum/7-in-car-entertainment-ice-and-security/

Had a look at the diagram, we tried most of the ways already with no result, one thing I didn't check was the ciggarette fuse as I've had one go in the past and it took out the stereo along with it.