These take 20 seconds to achieve working temperature and the vehicle operator had to manually time (or guess) when the 20 seconds had elapsed. With in-cylinder glow plugs, technological improvements included a warning light on the dash to indicate how long the preheating should last. Also the preheating phase was made to be automatically activated when the operator turned the key to the "on" position for a long duration; the glowplug relay switches the glowplugs on, and a light (see picture at right) on the instrument cluster illuminates.