fluid is permitted to escape from accumulator chamber 12 in accordance with the setting of the size of bleed orifice 44 once sufficient pressure is bled from accumulator chamber 12 diaphragm 14 moves back to the solid line position shown in fig1 to open contacts 16 and 18 the described system is operative to flash lights 24 even though the vehicle is not decelerating as when the driver attempts panic braking on a slippery surface takes place fig2 shows another arrangement wherein accumulator chamber 12 contains a movable piston 62 normally biased to the left by coil spring 64 a centrally located rod 66 extends from the piston 62 through a suitable hole 68 in the housing for accumulator chamber 12 to act against insulator 70 for closing contacts 16 and 18 when the rod is moved to the shadow line position in this embodiment bleed orifice 72 simply provides communication between accumulator chamber 12 and fluid supply chamber 28 for bleeding fluid from accumulator chamber 12 at a predetermined rate for maintaining the lights in a blinking condition for a predetermined time after the panic braking force has been released from the braking actuator 58 the arrangement of fig2 is a closed system facilitating use of hydraulic fluid in accumulator chamber 12 and supply chamber 28 fig3 shows still another arrangement wherein a fluid supply chamber 74 has deformable walls of elastomeric material and brake actuator 58 includes deforming means for deforming the walls of chamber 74 to reduce the volume thereof for forcing fluid therefrom through conduit 76 into a bellows 78 defining the accumulator chamber bellows 78 may simply operate against a spring arm carrying contact 16 for moving it into engagement with fixed.