Lucas “Step, Door or Boot” switches are used to switch on the lighting for the interior of a car, the boot (trunk) lamp, for a tool tray or even for map reading. These Lucas switch types were used in Jaguars of the period 1940 to 1960. Their construction is based on the use of a plunger with an electrical contact. When a door or boot lid is closed, the plunger is pushed inwards (against a spring) and the electrical connection with the housing (earth) is “off”. The switch is “on” when a door or boot lid is opened and the spring pushes the plunger (complete with electrical contact) back to the housing (which is connected to earth/car body).
Various Lucas switches will now be discussed in detail, whereby we have to state upfront that information is not always clear. Jaguar and Lucas may refer to different part numbers for the same application.
This switch model is probably the first applied Lucas “Step, Door or Boot” switch on (SS) Jaguars. According Jaguar publication J3 of December 1947, it was used on pre- and post-war 1.5, 2.5 & 3.5 Litre Jaguar cars during the period 1939 till 1948. The Jaguar code for this switch was BD.207.
This switch is known as Lucas Switch Model 88 and it is easily recognised by the thick mounting flange, with both the Lucas switch model number Nº 88 and Lucas “order number” 359236 on it. Note that the plunger is of the short type (about ¼ to ⅜” above the flange). It was probably delivered by Lucas with a cable already soldered to the contact.
According Lucas catalogue 400D and E, switch 359236 was later also used on the Mk V from 1946 till 1948 as a Boot Lamp Switch. This is not confirmed by the Jaguar SPC for the Mk V (see Lucas 33175 hereafter).
This is Lucas Switch Model 94 which has a (casting) number 372903 on the back of the flange. It was manufactured in two versions: with a short and a long plunger. The Lucas 31175 switch is the one with the shorter plunger and as such the successor of the aforementioned 359236 version. The 31175 can be recognised by a thinner mounting flange (compared to 359236). This switch was used by Jaguar as “Tool Tray” switch according the Mk V SPC, with reference to Jaguar code C.2614.
Lucas mentions number 31175 as the Boot Lamp and Step Light Switch used for the Mk V during the period 1949 to 1954. Jaguar however refers to their part number C.2614 with reference Lucas 31185A which seems incorrect (see Note under Lucas 31185).
This switch is identical to the 31175 switch, apart from the longer plunger (about ½” penetrating from the flange). This Lucas number is not mentioned in the standard Lucas catalogues, meaning this is a dedicated product made for Jaguar. The Jaguar code for this switch is C.2873 (a later code) and is mentioned as Boot Lamp Switch for the Jaguar XK 120 and 140. Note that the 31185 switch is stamped 31222 at the back of the flange (see later). We should not exclude the possibility that the 31222 switch was delivered by Lucas with a piece of cable soldered to the contact, hence the Jaguar specific Lucas part number 31185.
Very early alloy XK 120s have a different construction for the installation of this switch, using a separate earth cable under one of the screws. Later cars use a steel Plate BD.2391 (tapped for two 3BA CSK screws) without any extra earth lead.
Note: The Jaguar Mk V SPC refers to Lucas 31185 (Jaguar code C.2614) as a light switch for the tool tray, but the switch is stamped 31175A on the body. As this switch has the short plunger, this must have been the 31175 switch and not 31185 (which was later coded C.2873 for the Jaguar XK 120 and 140).
This long plunger switch is first mentioned by Jaguar as Door Switch for the Mk V with code C.2658 (an earlier number than C.2873 for the 31185 switch as defined in the XK 120 and 140 SPC’s). Lucas 31222 is listed in various Lucas catalogues and also referred to as correct for the Jaguar XK 120 and 140, although supplied by Lucas without a piece of cable. It has the Lucas casting number 372903 on the flange.
Lucas catalogue 400D refers already in 1954 to a switch 31404 as the successor of 31222. This is the “long plunger” type again. Note: in the Lucas 400E catalogue of 1960, the 31175 switch is still referred to as the “short plunger” type.
Switch S35122 on XK 150 DHC/FHC
In 1957 Jaguar completely changed the construction of the door switches for the interior lights on the Coupe models of the XK 150 model. This switch (coded C.9653) was no longer made by Lucas.