Your profile states a 2021 model. MOST newer(last 10 years) Trailers that have 3 sets of speakers, the Stereo itself has "A" "B" "C" speaker control and the Balance will operate on all 3 sets. Some of these Stereo's it is difficult to figure out HOW to engage the 3 speaker switches. BUT, If doing the balance kills 1 set, then it is probably miswired. It is common for the factory installers to miswire the speaker leads. I would take it b ack to the dealer and have THEM fix the wiring problem. POST the Brand and Model of the Stereo for us to give you more help. Doug