I decided to change the GPS. Today, I installed the support bracket in the panel. It went smoothly as the new one has the same footprint has the old one. I also made all the connexions for the power, serial and audio.
I tested some more the harnesses and found a problem on one of may warning lights that is wired per my drawing, but the drawing needs to be changed as it is not working as I intended. I will have to change one of the switches to get it right.