Firstly, what are the parameters of the drive of the new mobo?
Resolution, frequency, color depth, refresh rate, etc.
You can make it display on the screen from the menu.
So, the old mobo was able to display pictures on the car monitor.
Please attach another LCD monitor to the old mobo and ask about the same signal parameters as mentioned.
Identical: you have right, there is something wrong about the signal. You need some electronics.
Non-Identical: I have right and there is something about the settings of the display, you just need to set the parameters.