What is the most likely cause of a problem with the lowbeam headlights? They will only come On when the headlight control switch is turned to the On position and the ignition switch is in the Off position (with or without the key in the ignition). With the headlight control switch in the On postions, when the key is inserted into the ignition and turned to either postion the lowbeam lights will not come On. The highbeams work fine, but in this model truck the highbeam headlights are different headlights from the lowbeam headlights.