Well I thought the bad luck was supposed to be yesterday.

I had a spare wire from original install from the amp rack area. So, I used it direct from bus bar to power the HU yellow. All good - checked and everything working properly.

Then, went to mount everything back up tidy - HU, Exile ZLD, and zip tie wires. Now - amps and ZLD won’t trigger on when HU comes on. I don’t get it.