I would say it could be both lift interupt and the multi-function switches. The truck could have more than one problem. It could also be a loose or bad conection at the box that hold the cards that operate the hydraulic functions, broken wiring to the sequencing switch ( the push button switch on the handle),or the sequencing switch wired incorrectly. The wires to the sequencing switch breaking inside the insulation where the control handle rotates up, down, right, and left is a common problem on these trucks.