You actually need 2 adapters:
1. Minn Kota Univ Sonar 2 Adapter Cable Garmin 8 pin MKR-US2-14
2. Garmin 8 to 12 pin adapter PART NUMBER 010-12122-10
I presume you are connecting to the MK US2 transducer built into the trolling motor. This is what I used and it works.