When the Series III head came out in late 1982 it looked to have some very promising features. The three position height control was one of them. But that was over 25 yrs. ago and things have changed quite a bit since then,with potentiometer systems. There are still quite a few Series III systems still running and the adjustment on the control is pretty simple. Normally the plastic controller is reliable and and only breaks due to wobble box belt rubbing on lH end,out of adjustment turn buckle, or a header that has sat out in the elements. We usually add about 2" of wire to end of each blue and red harness wire so it will have more flexibilty when controller is moving. We have seen these wires break internally and give grief on a header controll that only works part of the time. Once controller is on head with header in the up position,grab a hold of the first finger under cutterbar and raise finger up so it touches bottom of feather sheet.At this time the bottom spring should just be touching front bar of controller. Check both ends if you have an early 20ft. since they had two controllers and the later ones went back to just one controller. Make sure and add the PVC behind the cutterbar as this will make it feed a whole lot better. If header has sat around for a while then I would disassemble conveyor slip clutch and clean all the rust off of surfaces and take some emery paper to clutch disc to take the glaze off. Stainless feather sheets are another nice addition. Still a decent header if someone has taken care of it and should work well with some minor tweaking. Hyper Harvest II