In their Catalogue 400E, Lucas refers to the use of 3 different wiper switches over the life of the XK 120. The first is PS.7 with Lucas code 31288 and the third version is PRS.5 switch with Lucas code 31304. Both well-known and well documented.
According Lucas 400E there was yet another PRS.5 switch used with Lucas code 31391 on the “Sports” model during 1953-1954. This version had a short life as it was replaced by Lucas 31304 still within the year 1953. There are many 1954 OTS versions that have the later Lucas 31304 switch (including my own April 1954 built OTS) so the time frame provided by Lucas is probably too long.
Much to my surprise, Bernard Viart in his book “Jaguar XK 120 explored” shows on page 217 of the Revised Edition, a drawing of this switch (Lucas 31391A) with date code March 1953. We know that Viart used original Jaguar parts to photograph and make a drawing on basis of these photos. Unfortunately Viart does not refer in his book to the third switch Lucas 31304 at all.
Does anybody recognize this particular switch Lucas 31391 and/or has a photo of it? As it was used for only a short period, I’m looking for information whether it was used on the OTS and/or the FHC and what year (or even chassis number if possible). Lucas 400E mentions that it was only used on the “Sports” model which is the OTS I assume.
The attached photo shows (most likely) the switch in question, but the stamped number is very hard to read.
So your Nov. 1951 FHC still has the “old” PS.7 switch Lucas 31228, complete with chrome knob. This is perfectly in line with the Lucas 400E information that all XK 120s used the Lucas 31228 over the period 1949-1952. Only from 1953 the PRS.5 switch 31304 was used.
I just discovered that my own April 1954 built OTS has the Lucas 31391 switch!!! As most books indicate that the final instrument panel change took place in March 1954, I assumed mine would have the “final” switch Lucas 31304 according the SPC, but this is not so: it caries a Jan 1954 built Lucas 31391A switch. Always check twice (I have to say to myself).
Any other “sightings” of the Lucas 31391 switch? And do others have indeed the 31304 switch on their (very) late XK 120 OTS instrument panel as the Jaguar SPC says?
Bob, the dedicated “1954 Jaguar” Lucas catalogue (Publ. CCE906, Jan 1954) adds to the muddle, but it at least has another view of the switch, suggesting perhaps that 31302, 31303, 31304 & 31391 look very similar.
I just wish I could summon the enthusiasm to examine the switch on my June ’54 FHC.
Where’s Roger when you need him?..
Chris T.
Chris, I think the 1954 Lucas Catalogue might indeed add to the muddle. The images for the two PRS.5 switches appear to be reversed. In my experience, the PRS.5 switch mechanisms supplied to the XK120 and XK140 were paired with a metal switch body having the extended threaded boss of approximately 3/4 inch. The PRS.5 switch mechanisms supplied to the Mark VII were paired to a metal switch body having a short threaded boss of approximately 1/4 inch.
The PRS.5 switch mechanisms and the PRS.5 metal switch bodies could be mixed and matched for specific requirements. For example, the switch mechanisms were made in two, three, or four position varieties depending on the needed function. The metal switch bodies were made with either a long or short threaded boss depending on the depth of the instrument panel.
Thanks for these sheets: didn’t have them yet. They confirm what Lucas mentioned in the 400E catalogue, but even mention that the final XK 120s FHC/DHC had the Lucas 31304 switch.
I’m preparing an article for the XK Gazette (Porter) magazine on the subject of XK wiper motors and switches. Mainly because there are so many errors in these “books” that I thought it’s time to correct these.
This is (another) photo of the “real thing”. The picture in the Lucas 1954 Jaguar document seems correct (when I hold the switch in the same position as presented in the catalog). But judge for yourself on basis of the following photo.
Bob, your photos show the PRS.5 wiper switch (Lucas part number 31391A) with a long threaded boss and two brass nuts, which is correct for the XK120.
I see the 1954 Lucas Catalogue showing the PRS.5 switch (four Lucas part numbers including 31391 and 31304) with a short threaded boss and one brass nut. I maintain the short threaded boss PRS.5 switches were not supplied to the XK120.
Here are photos of a short threaded boss PRS.5 two-position switch from my collection. It is Lucas part number 31304A, date stamped 10 52.
This appears to run counter to your assumption from yesterday that late XK120s were supplied with the 31304 switch. I think there must be an error in either the XK120 Spare Parts Catalogue, the Lucas Catalogue, or both.
Checked and agree with you that the Lucas 31304 has a very short threaded boss. See this photo to confirm your statement. Although the number stamped is a bit “double” this is a later 31304 with suffix B and date code 1 58 (I guess).
So another problem indeed. One of the possibilities could be that Jaguar (and Lucas) referred to the 31302 switch (as used on the Mk VII) but I checked and this switch has a short threaded boss as well. On the other hand, when you look closer to the instrument panel of the Mk VII with this switch you’ll see that the switch is mounted with the nut to the steel instrument panel, not to the wooden facia. So only the (thinner) stem (without thread) is running through the wooden part. See photo of Mk VII.
Could this be the solution? I don’t have the latest instrument panel for the FHC/DHC (C.8395 I believe) at hand but may-be someone can check or even remembers whether the wiper switch is attached to the instrument panel and only sticking through the wooden part.
Searched for more evidence, but I guess that the longer threaded boss with two nuts can be positioned further back, provided the wiper knob and the corresponding part of the switch are long enough. I also observe switch knobs that are closer to the wooden facia panel while others are further away.
There is of course also the recessed section at the back side of the wooden panel to give some additional room for positioning the switch back or forth.
See these two photos with a different knob position.:The second pic is XK 140 or 150.
Bob, besides the ability to adjust the wiper switch knob “fore and aft,” having one brass nut on each side of the sheet metal panel makes it easier to loosen the wiper switch for removal and service later on. But in reality nothing is easy when it comes to servicing the switches, instruments, wiring, etc.
It’s hard to believe the Factory consciously decided to make it easier to service the wiper switch while at the same time not addressing the rheostats, which are nearly impossible to remove for service.
I do think the short threaded boss wiper switches can be used in an XK120. I just don’t think the Factory used them.
I’m currently assembling a XK120 FHC (late) dashboard, and though I see references in this thread and in some of the standard references that the PRS7 31304A fits, I don’t think that is true. The short threaded boss doesn’t allow the switch to back off from the metal mounting plate far enough, leaving the knob protruding too far in front of the woodwork. Maybe this is the significance of the “A” in that number? Was there a straight up 31304 that had the long threaded boss? Opinions?
The Lucas 31304 still remains part of a mystery. My April 1954 OTS instrument panel has the Lucas 31391A with date code 1 54 and it fits well (see earlier pics above).
The A suffix (as used by Lucas) is in fact a date code and indicates that this was the first Lucas 31304 batch of wiper switches produced. It was followed by suffix B, C etc. Some Lucas parts run up to suffix H or even higher (I’ve seen the letter K).
If I’ve solved all the problems I’m having right now with the assembly of my XK 120 OTS, I might return to the Lucas 31304 wiper switch and investigate why it was listed by Lucas for the XK 120.
But the fact that Lucas listed Wiper Switch 31391 for the “Sports” model during 1953-1954 allows me to proceed with the assembly of the electrics of my car (very selfish, I admit).
.
Bob K.
Yep, interesting (if this sort of thing runs your motor, otherwise one probably doesn’t belong on this list!). I’ve also got the 31391A in my 1953 SE FHC and it fits well. The 31304 simply would not work. --Dave
