to engage 4wd whilst red knob lever is pushed forward in high ratio just push down on yellow knob it can be done on the move but not if a rear wheel is spinning , to come out of 4wd stop and pull red knob lever fully back to low ratio and yellow knob should pop up ,push red knob lever back in to high you are now back in 2wd ,in you just pull red knob lever back to low ratio you are in 4wd at all times irrespective of yellow knob ,only high ratio has selectable 2wd or 4wd ,dont use 4wd on hard surface like roads