Connecting inputs without obd.

As the title suggests, I have a car without obd. I have an aftermarket engine ECU and can use realdash via Bluetooth on my phone. Most of the dash works very well but I’m now at the point where I want to replace my old instrument cluster with realdash. My plan is to use a raspberry pi with Android and it should hopefully work as well as it does on my phone. However I’d like to get the indicators, warning lights and fuel gauge to work. These are generally 12v on/off signals other than the fuel gauge which varies from 0-12v. How and what would be the easiest way to connect these to realdash? Is it as simple as using a gpio circuit board? And would I connect this to the pi or engine ECU? Thanks in advance.

I solved this issue using the RealDashCAN protocol and connecting Arduino nano to my protocol))) it’s easier not to

Thanks for the reply. Unfortunately my car doesn’t have any CAN either. I’d like to know how you have yours set up. It looks very clean.