I have been getting this code for some time after some internal mods and it's driving me crazy. It's normally a generator L-terminal circuit code, but the charging system is new and it charges great. I have checked all of the connections and cleaned the contact points to the alternator. The manual shows that there are messages with this P1637 code.

Any idea what the messages are? Maybe that will provide some data to steer me in the right direction to clear this up. TIA.