GB1421739A - Vehicle electrical systems - Google Patents

Abstract

1421739 Road-traffic signals on vehicles CAV Ltd 6 Feb 1973 [19 Feb 1972] 7782/72 Heading G4Q A vehicle lighting system (for use with a tractor and trailer) is of the kind comprising a load-sensitive unit (such as a flasher) controlling or sensing current flow to a first lamp from a first supply point, and being adapted to have a second lamp connected in parallel with the first lamp whereby a third lamp is connected to a second supply point; and has means for sensing the connection of the third lamp and for modifying the operating characteristics of the said unit. When switch 15 is closed (Fig. 1) a flasher unit 20 controls direction indicator lamps 22 on the tractor and 24 on the trailer. In order to maintain the flashing rate unaltered when the trailer is coupled up the flasher 20 is earthed through diode 26 and lamp 25, the adjustment of the flashing rate taking place in known manner in response to the earth connection. The current passing through the lamp 25 is insufficient to light it. When lighting switch 13 is also closed the trailer side and rear lights 16 are lit and also the trailer lamp 25 and the diode 26 is now reverse biased. However the current in lead 14 energizes relay coil 19 to close contacts 27 and again connect the flasher unit 20 to earth. In an alternative arrangement (Fig. 2) the relay 19 is replaced by a resistance network 30, 31, 32 so that when current flows through lamp 25 a voltage is tapped off to forward bias P-N-P transistor 33 and in turn forward bias P-N-P transistor 35 which acts, in place of the relay contacts 27 to earth the line 28.