XK 140 Light Switch WTF

Ok so doing some much needed wiring updates ie adding an alternator and fog lights to the existing original wiring harness where all wires are brown and no two wiring diagrams are alike. The light switch has terminals 3, 4, and 6 best as i can tell and on the first click of the switch it closes 4 to 6 witch does nothing as the #37 feed wire is on #3. Second click closes 3,4 and 6 giving you side lamps and head lamps, third click opens #4 leaving 6 and 3 closed giving you side lamps only with optional fog lights through its own switch. I ordered a 4 position switch for the fog light option but what am i missing on the first click of the switch it does nothing. I could almost use the three position switch for the fog lamp option and just elimanating the side lamp only option because really when do you drive with side lamps only (never). I have 37 on 3, 1 on 4 and 41 on 6 could not find the right info in the search option.

I could find only one diagram for the XK140.


It looks to me like the terminals on the switch are labeled 6, 7, 8, 10, and 11.
color 37 brown/white, two wires on 6, going to the key switch and ammeter.
color 1 blue, one wire on 7, going to the dipper switch
color 41 red, three wires on 8, going to the fuse box (which leads to the side lamps), panel light dimmer control, and fog light switch if fitted
terminal 10 is not used
color 42 red/yellow, one wire on 11, going to the fog lamps if fitted

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In period the sidelamps were also known as parking lamps in Britain, which is a clue…
Leaving an unlit car at the side of the road in dark, wet, foggy and crowded London was asking for trouble.

Same here, some people drive around with their parking lights on until the sun is well down.

When I was a student in London in the seventies, nobody used headlamps. It was sidelights right through the night back then - it was never really dark and the streets were well lit.

We have such people in the Chicago suburbs today. Even no lights at all, there are so many street lights that they forget to switch them on. Flashing your brights at them usually doesn’t do any good, just makes the guy behind them flash back at you.

Getting back to Tim, any luck figuring it out?

Well yes sort of I did find that the first click of the switch makes makes three contacts one of which is number 11 that i did not notice befour because it had no screw or wires on it. Anyway that would allow me to run head lights and side lights on the first click, then fog and side lights on the second click, and lastly side lamps only on click three. 3 clicks should of been my clue the car must of came with the fog lamp option ss there is also a SB40 relay that i have not known what it did until now its for the fog lights. The thing is my nomenclature is backwards from the OSHF TO OHFS, kind of makes one go ummm. Be interested to see what the new switch does as far a sequence should be here today.

It was the accepted norm in London - even the police didn’t use their headlamps. It actually felt safer - you could see other vehicles clearly without being dazzled all the time by full lights. Can’t remember if it was a legal requirement back then or not. Obviously this was long before the days of daylight running lights, and now the car switches the lights on for you anyway…

Tim, the lamps should come on in order - off with the original switch pointing upwards, then sidelamps alone, then side and head, then side and fogs. British cars never had the option of headlamps without sidelamps, at least not in the home market. Headlamps usually go off when foglamps come on. So OSHF is correct.

I’ll be wiring mine shortly so will report back - although I dismantled and rebuilt the original switch, as the repro didn’t seem as well made. My original switch just spun on its spindle as the cam giving it the four positions was worn down, had to build it back up with resin then file back to shape.

Roger,
Didn’t leaving the parking lights on all night drain the battery?

They had a single light for that.

And in an example of poorly written vehicular laws, at one time Illinois had a law that said you could not drive at night with the parking lights on. It was in the driving instruction book the DMV issued for high school driving class. They meant of course that you had to switch on your headlights, and at that time with all American cars the parking lights went off when you did. But my British Mark V parking lights of course stayed on, so I got a lot of guff from my high school buddies about being in violation.

Back to Tim, the terminal markings don’t seem to be standard; can we see a picture of these switches?

Yes, often.

It’s still a legal requirement in the UK to display parking lights when parked in an area with a speed limit of over 30mph. You also should be facing in the correct direction i.e. with traffic, and a certain distance from a junction. The law changed in 1955, but I can’t find out what was required before then.
The little ‘clip-on’ lamps like in Rob’s photo were not always accepted, as I remember. Depends on the copper* you’re dealing with!

*See also Bobby, Rozzer, Pointyhead etc.

Mine are not clip-on, there is a 3/4" hole in the canopy.
We had a discussion about this law on pre-xk.

Nice little Marchal light!

When I earned my Virginia drivers license in 1967, the requirement was to switch on the parking lights at dusk. At sunset, the requirement was to switch on the headlights. I recall my parent’s constant back-seat driving to “make sure the parking lights are on now that it’s dusk.” And then a little later, “better switch on the headlights now that it’s sunset.”

However, there was no requirement to use the parking lights while actually parking - only while driving.

On my 140OTS terminal 4 is the hot feed. #1 goes to the sidelamps, and #8 to the headlights. When I bought a new wiring harness from (I think) British Wiring) the schematic that came with it did not work. The headlight switch arrangement was not like other schematics I had seen, and I think the 8 terminal directional relay was backwards.

Yesterday my XK120 was on display at the local Jaguar dealership for their annual customer appreciation event. I returned home well after dark and needed to parallel park in front of my home for a few minutes while I rearranged my garage. Even with a street lamp about 100 feet away, I was amazed how “invisible” a dark colored XK120 becomes when parked at night. There are no reflectors built into the tiny tail lamps. Just a few glints of reflected light from a small amount of chrome at the rear is all there is to warn passing motorists. The next time I do this I’ll leave the side lights switched on.

The new switch arrived today,yea but it does look a little sub standard. There are no marking for the terminals I has to make up my own to check sequence of operation but then was easily able to get 3 clicks of the switch to match the OSHF pattern. Can’t describe to well as I say had to assign numbers to them myself. Comes with no diagram of any kind as well so your on your own with an ohm meter to get it figured out. Once done though very easy to complete and it does have two raised posts for the number 37 wire input and the number 1 head light output that you can fit a # 12 wire connector no problem. My old switch had a bad contact on the first click that would not allow me get the proper sequence. Thanks for all your help and just saying if you run side lights only in my neighbor hood your likely to hit a cow.

Not many cows in central London - the only place in the UK where I used to drive on sidelights only.

I had one of those repros, and eventually decided to strip and repair the original. Wasn’t difficult, ultimately - but I did build up the raised bakelite ridges the detent runs over to make the action more positive.