The XK 140 SPC Publication J.15 of July 1955 lists only one wiper switch knob: C.4664 (Lucas 316.646). But Lucas catalog 400E refers to yet another wiper switch knob for the XK 140: 318.168. This might be a later knob for the XK 140 which could be replaced 1 : 1 for the early knob, meaning Jaguar did not change their part number.
I observe that early 140s have a wiper knob with a text lay-out, whereby the H N P start at "9 o’clock”. In 1956 we see a number of XK 140 instrument panels with knobs that I would call the “10 o’clock” lay-out. See pics below.
Are there XK 140 owners that can help in getting a better insight whether my assumption is correct? Does your XK 140 have one of these wiper knobs and what was the built date of your car?
Your help is much appreciated.
I’ll look at my Oct., '55 build-date car when I get a chance. Notice the difference in the gaps between “positions”…could the tighter spacing actually mean a shorter throw indicating different switches were used?
Yes, I guess you’re correct. There was a change-over from a PRS.5 switch (XK 120) to the PRS.7 switch for the XK 140. This switch is listed as a “three-way” PRS.7 switch Lucas 31427.
I don’t have the PRS.7 switch at hand right now, but the “steps” between the positions might be smaller for the PRS.7 switch compared to the PRS.5 version.
But as this PRS.7 switch was used for the entire period the XK 140 was in production, this would imply that for the first knob Lucas 316.646 the markings would not be in line with the positions. Can’t remember whether that was the case on my 1955 XK 140 that had the “9 o’clock” knob.
The 318.168 knob was also used on the TR3 and the AC Cobra (so even after 1960 when Lucas said it was superseded by another knob).
Bob, I assume these are PRS.7 switches, although they do not have a specific marking to indicate it, as found on the bottom of the PRS.5 switches. The bottom of these switches is simply marked Lucas England.
The operating shaft of these switches is not offset like on the PRS.5 switches. The operating shaft is centered in the switch body. However, the switch body itself has the same dimensions as the PRS.5 switch body.
Like the PRS.5 switches, these were made with either short-threaded boss or long-threaded boss switch bodies. The switch on the left is a four-position, stamped 31426B and dated 3 58. The switch on the right is a two-position, stamped 31546F and dated 6 60. (I don’t have a three-position version as might be found on an XK140 to operate the wipers.)
Here’s a view of the bottom of these assumed to be PRS.7 switches. The switching function appears to be a more robust design compared to the PRS.5 design.
Thanks for thinking along with me on the subject.
I’ve never opened a PRS.5 nor a PRS.7 switch, but looking at the backside I count 8 positions (not all are used) in 360° on the PRS.5 and 12 positions on the PRS.7 switch. This would mean that in case of the PRS.5 switch every “click” represent 45° and for the PRS.7 this would be 30°. So two clicks on the PRS.5 means 90° and on the PRS.7 only 60°.
This would explain the “9 o’clock” text lay-out on the PRS.5 and “10 o’clock” for the PRS.7 knobs.
It would also mean that the early knob Lucas 316.168 is in fact a PRS.5 knob used on a PRS.7 switch. May be that’s also the reason why Jaguar asked Lucas for a similar knob (Lucas 318.168) but now suitable for the PRS.7 switch.
Does this make any sense? Is there an owner of an early XK 140 who could confirm that when the wiper switch is turned two clicks, the angle is about 60° and the “H” is not on top?
I have a 140 with a build date of November 20, 1956. The switch is stamped 314270 and is dated 7 56. There are 11, not 12, positions on the back, 6 of which are used. The knob is the same as the second one posted by Bob K. above which correspond to the switch’s three positions. Each letter is at the 12 o’clock position when selected. The back does not match either of the switches in Mike’s photos.
Hopefully, you can enlarge the table below enough to make it out. The table matches switch knobs to the switches used by Jaguar. The table shows two different wiper knobs and two different wiper switches - 31427E and 31302D (one for an XK and one for a saloon).
The first image below seems to confirm the center shaft, long-threaded boss switches used by Jaguar. I think we can assume these are the PRS.7 switches. I maintain these were the type used on the XKs.
The second image below shows that Jaguar also used two short-threaded boss switches. The upper switch appears to be a PRS.5, and the table above shows it was a wiper switch - likely for a saloon.
The lower switch appears to be a PRS.7 center shaft (31428). Looking closer at my own switch, it also appears to be stamped 31428B - not 31426B as I stated earlier today. The table above shows it to be a (4-position) headlight switch. Again, I maintain for a saloon. The table above shows a second headlight switch (31426H). And the image directly above shows 31426 as having the long-threaded boss (for an XK).
I have stared long and hard at these switches. My 140 has the same 31427 with the long bush, as Bob’s. The PRS series (I guess this stands for Panel mounted Rotary Switch) are generic types, the actual switch function can vary a lot as noted by previous contributors. PRS7 appears to be able to host up to twelve terminals although confusingly, the terminals are marked 1 to 13. ( There is no terminal 9). 31427 has 11 available with a space where terminal 2 would go. There are four interconnections on this switch.
I worked out the wiring once a long a time ago and drew diagrams that made sense of it with DR1 or DR3 motor connected. It’s still on my website if anyone’s interested DR1 Motor
Thanks for this info: I guess you’ve solved our problem for 99%!
So, your November 1956 built XK 140 has switch Lucas 31427D manufactured some months earlier (July 1956). When I referred to 12 positions I mean that the engineer at the drawing board first draw a circle and divided it in 12 equal sections (every 30°) . That he didn’t use all 12 points for contacts etc. doesn’t really matter.
The knob you show (assuming it’s from your 1956 car) means that this is (most likely) the later knob Lucas 318.168 that replaced the earlier knob 316.646. You state that your knob exactly matches the “clicks” which means that it was developed for a PRS.7 switch.
All we need is now is a confirmation that the earlier XK 140s (that all had this 31427 switch) have a knob that doesn’t have each letter at the 12 o’clock position when selected. That would proof that Jaguar started indeed with a PRS.5 knob on a PRS.7 switch.
Regarding the 1961 data: switch 31427 was continued for the XK 150 so still mentioned in 1961 seems feasible. Lucas switch 31302 was used from 1952 onward on the Mk VII saloon, which had a two-speed wiper system. This switch is a PRS.5 switch with 3 positions.
What built date is your 140? Does it have the early or later knob?
I remember your wiring schemes very well. They saved me, when I had problems in reconnecting all the wires to the wiper motor after an overhaul of the motor.
My XK140FHC build 7-Jun-1955
Has the “10 o’clock” lay-out.
But I am wondering if this dash is really original for the above build.
As some parts come from another 1957 XK140 ( most clear are Engine/Gearbox )
According to the factory records, my car was completed on 5th November 1955 although not delivered to the supplying dealer until 10th May the following year. During this period, it remained at the factory and its original low compression engine was changed to an 8:1 engine and the factory records amended. Its original 7:1 engine went to Zambia. This resulted in an engine number out of sequence with the body number which puzzled me until Messrs. Payne and McGrath explained what had happened. It must have been given a new commission plate by the factory because the numbers on it match what the car has.
Sadly, I can’t tell you anything about the knob as the entire set disappeared while the car was in a professional workshop along with the original indicator and ignition tell tales. I had to replace the whole lot with repros from Barratts.
Support your thoughts as my August 1955 XK 140 still had the “9 o’clock” knob Lucas 316.646 and it was “untouched”. And this car was even later than yours.
That’s very valuable information. This would imply that the introduction of the “10 o’clock” knob on the XK 140 would have taken place somewhere between August and October 1955 (if my and your knob are original to the cars). This would be roughly one year after XK 140 production started and sufficient time for Lucas to manufacture a proper “PRS.7” wiper knob for Jaguar. I’ve added photos of these two knobs and it’s clear that the same “font” has been used for the text on both.
