So i spent most of today connecting my speakers to my old JBL 75.2 amp (took far longer and took apart a lot more of the car than i'd anticipated) and now the amp is installed and the speakers are powered by it. It's working, as if i connect my phone to the input red/white cables i get music loudly playing out the car speakers.

For some reason my headunit has decided to die though, no power and nothing lights up. I thought it could just be the headunit so hooked another one up and still no power (now tried 3 different headunits). The strange thing is the remote wire is obviously connected to the headunit and it still powers on the amp, however the amp is continuously powered until the headunit is physically unplugged from the cars ISO plug

I've tried disconnecting the amp so the car is how it was before i started doing anything to it (excluding the speakers being wired to the headunit, but i don't imagine that would make any difference) and haven't got any idea what else i can try

Help please!