Installing a Fishman bridge is made much easier with their PowerChip, which serves as both a volume control and a smart switching device. The PowerChip can detect whether you’re using a mono or stereo cable and adjusts by splitting or not splitting the signal accordingly.
When setting up, focus on your piezo and magnetic signal chains as separate entities, knowing that they will ultimately join together through a switch. Start by configuring your magnetic pickups and piezo system independently, then connect them using your chosen switching device—most commonly, a traditional toggle switch.
As Artie mentioned, Fishman’s website offers a wealth of valuable information to guide you through this process. And as Mincer pointed out, it’s important to consider the specifics of your guitar, magnetic pickups, and the particular Fishman bridge model you’re using for optimal results.