You need to check the 2 brake switches. Very small switches. When the 3300s first came out they didn't allow you to replace or adjust the switches. They even made the local SEC branches buy the entire brake instead of replacing the switches. I believe they changed their minds after realizing how much time and money it was costing them. Later the switches became available to SEC techs, but I never heard of any announcement that they were officially allowing switch only changes. The switches have 2 small metric bolts and nuts for adjustment. You'll find they have marks on them that will show if you've adjusted or not. That is just my understanding of the situation and not a recommendation of any sort.