New Amplifier won't power up

Just installed a new amplifier in my RV, running the amp and the head unit direct off the leisure battery. I am not getting power to the Amp from the Head unit Amp turn on lead. I have checked the voltage and it is -0.03 at head unit cable and -0.08 at amp terminal block. the amp feed direct from the battery is fine. Any ideas?

I am thinking about running the Amp to head unit wire direct from the amp to the battery and using an inline switch to power it on/off thus bypassing the head unit altogether and not draining the battery when not in use, Is this a good fix?

Also, I have run the Ground wire from the amp to negative terminal on the battery, Is that ok?

Thanks
Dave

are you SURE yopu are not wired to the solid blue antenna lead ? It only works when the radio is on.