I bought my Formula with the SmartCraft SC5000 and Stainless Marine mechanical trim indicators. The bracket for the mechanical trim indicators replaced the original trim sending unit. Formula just clipped the wires and installed the bracket. Everytime I started the boat I would get a trim sensor fault. Worked with Formula and Mercury to try everything to get rid of the fault, but the software didn't allow it. Stainless Marine came though by designing a bracket that also allowed the original trim sender to be mounted, but even after that it STILL gave a fault when turning the key on. Ended up that the SmartCraft unit needed to go through a complete rebooting process. Not exactly sure how to do that as it was done at a dealer. I recommend looking into that. Good luck!
Oh, and I do remember it took multiple calls from the mechanic to Mercury tech before finally finding someone that knew what the heck to do. This was in 2006 and it seemed like very few people knew anything about SmartCraft. Hopefully that has changed...