The mechanical portions of the system mounted onto the frame and equipped with all of the appropriate airlines. There are five slots in the ECU, one for each of the air springs (labeled LR, RR), and one for the auxiliary line (ACC). The black tube is routed from the compressor’s head to the ECU (labeled IN). The remaining fitting on the ECU is an exhaust line, labeled EXH. Adding a line to this port is optional, but will reduce the exhaust noise. The red line coming from the body of the compressor leads to the inlet air filter (see page 72).