Let me explain further...... TIU track "A" using variable channel 1 works as does TIU track "B" using variable channel 2. If you operate the engine in the power district powered by variable channel 1 and choose TIU track "A" on the handheld it works. As you move into the other power district powered through variable channel 2 and then change the handheld to TIU track "B" it works. However, if you select "ALL" TIU channels only TIU track "A" will work but only in the power district powered through variable channel 1. When under "All" The engine will run through both power districts but when it is in the district powered by variable channel 2 you cannot use the Bell, Whistle or Direction control under option "All". .