I'm fitting a kenwood stereo in my fabia and I've for all the wires bar the antenna and I've switched the red and yellow leads but the headunit won't power on the laser for the disc moves so I know there's power going to it do I need the antenna to ground the head unit maybe?

Is the HU new? Have you turned the ignition on?

Yea and tried it with and without ignition on and nothing I've had to refit the original skoda tape deck for now