the detector 16 may be of any advisable kind known in the art for the sake of better understanding fig4 illustrates a further embodiment whereby the detector 16 is mainly composed of an electro mechanical contact element 24 which is pivotally mounted at one end 25 of the trolley 17 and is held between two electrical contacts 29 and 30 near the other end 26 of the trolley 17 by means of the springs 27 and 28 if during the displacement of the trolley 17 the contact element 24 contacts a fallen drop wire 5 the contact element 24 will be displaced and establish an electrical circuit through the contact element 24 and one of the contacts 29 or 30 to generate a dropped wire location signal according to still another embodiment the detector 16 may be composed of an inductive or capacitive proximity switch the previously described drop wire locators 7 are preferably equipped with a switching off element not illustrated in the figures which is controlled by the detector 16 already mentioned in such a way that as soon as the detector of the trolley 17 comes into contact with a fallen drop wire 5 its actuation system 15 is stopped by this switching off element thereby stopping the movement of the trolley moreover the invention also includes an indication means which indicates the location of the detector 16 of the movable support element according to a first alternative embodiment the indication means may be composed of a lamp or an indicator which is moved for instance below the plane formed by the warp threads simultaneously.