Working thru some problems on my MKII and my brake lights are always on?
Found the brake light switch and it reads .2 ohms so it looks to be shorted out. Checked the shop manual and the part number appears to be C16062-A.

This seems to be used in a number of other cars to like some MGB, Triumphs, Austin Healey, XKE, XK140 and XK150. So a pretty common part.

Online price is only about $15 but is there a common application like a Ford,Gm, Toyota that I can get at my local parts store?

Anyone change one? Did you have to bleed the brakes or just do a quick swap? Much brake fluid loss?
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Don't know if there is a generic switch that would be cheaper, but re fluid loss, there will be very little if you prepare everything first then just pop one out and the other in, you should be ok not to bleed that brakes after, but check what the pedal feels like before and then after you fit the new one, if it is softer, then you will need to bleed it I'm afraid.

 

Thanks for that and I will just order the right switch. They are common.

Any chance the brake switch is good and I am somehow trapping pressure in the brake system? I don't have any way to check if the brake system contains pressure or not?
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Highly unlikely that there is pressure in the system, I assume that the brakes come on and off ok ?

If the brakes release, then there is no pressure, alternatively you could unscrew the switch until you see a small amount of fluid coming out, and then check the resistance, you know for sure there is no pressure then.

It is common for these to fail due to arcing which forms a carbon track either shorting the contacts or melting the plastic and stopping them making contact.

 

Hi

These switches are notoriously unreliable, and I found on my car and have read, that it takes a lot of brake pressure to activate the lights, meaning you're braking but the people behind you are not seeing red.

I bought a generic motorcycle brake light switch, activated by spring pull, and attached it to my brake pedal, then spliced the wires into the existing circuit.

So now I have a "modern" style brake switch that activates as soon as thought the pedal. No brake bleeding required.

Might be something to consider.

 

Good point Don, MK2 did the same thing Brakes ? Valve Chatter, this eliminates the issue of these problematic switches.

I am looking at using a solid state pressure switch as an option, but not finalized that train of thought yet.

 

they are cheap enough, I get them on eBay for $7.00 and free shipping. Those were used in US domestic cars too.

some come with male spade terminals, others with screw-on terminals, but otherwise the same switch. So just buy 2 and keep one in the spare parts box.

to replace: loosen the old one;

with the new switch in one hand, turn the old one until it comes off and rapidly screw on the new one, no bleeding needed, you will lose perhaps a drop or two of fluid in the quick exchange. The new one should last 1 or 2 years then KAPUT!
well they sure last a lot longer than a gallon of fuel!

 

Yes brakes seem to working fine and they do release.

That's an interesting comment on the brake pressure required to activate the brake lights.

I recently completed a 1949 IHC pickup and they use a low pressure brake switch. They are available but not common. So on that truck any parts store brake switch would screw in but like you said no brake lights unless you were really pushing hard on the brake pedal. That was the first time I had heard of a low pressure brake switch.

I wonder if the MK2 needs a low pressure brake switch?

https://www.summitracing.com/parts/prf-80174
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The switch on the Mk2 should come on at 20 to 30 psi (in the Lucas spec.)which is quite low in terms of pressure, I think the burst pressure is somewhere like 3000 psi !

 

The switches supplied by the typical vendors don’t seem to have a very long life. I have installed this one from Ron Francis Wiring. It is supposed to be higher quality and intended to operate effectively for a longer time. Whether the claims will be proven true - well, only time will tell. As you can see it is more expensive than the switches commonly used.

https://www.ronfrancis.com/prodinfo.asp?number=SW%2D32

Lin

 

Well that complicates things even more! There is a number of low pressure switches but they have different pressure ratings? Glad to hear the Lucas rating as that's what was stock.

I hope the one I got on EBay is low pressure but it does not say. I sent the seller that question.
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I had a problem with the Brake lights on my 1965 "S" type, but it turned out to be a poorly crimped connection-one of the two wires was not making an electrical connection with the switch! BUT-thinking about brake light switches failing, I have replaced most of my bulbs with LED versions, they will take far less current to operate, and so should extend the life of the brake light switch. However, here in the U.K., and referring to conventional "filament" brake light bulbs, I have rarely come across a brake light switch failing in service, so i wonder if this is a bit of a 'red herring"?

 

This particular type of switch has very little movement and are well documented to cause issues due to arcing, as the switch is analogue in nature of operation, unless you stamp on the brake, the switch closing is relatively slowly, there is no built in "toggle" off or on, the pressure pushes a diaphragm until the contacts make and with 2 x 21W lamps this is 3.5 Amps, plenty for a nice little spark on contact.

LED lamps will definitely prolong the life of these switches, there are also plenty of cheap reproduction switches which carry the Lucas name, unfortunately the name Lucas no longer guarantees some level of quality after the demise of Lucas itself and the licensing of the use of the name.

 

when I bought my S type in 2004 the brake lights were also staying ON, it was the screw-on switch, I replaced it and done.

But as to the point of requiring that the pedal be pushed hard to get the brake lights to operate, I never had that problem, once the switch was replaced the brake pedal force required was / is actually little, they come on on the first 1/8" inch of travel of the pedal.

What I was more concerned about was the location of the brake lights, at the lower section of the tail lights.

then I found out that the bulb receptacles are removable from behind the tail light assembly, so I inverted the brake-driving light receptacles with the turn signal receptacles, so that the brake-driving lights are now on the TOP section of the tail lights, and the turn signals are now at the lower section, a quite visible improvement at night.

then I went a step further and had the lower section LENS replicated in Amber, and I love the way the car looks now. Jaguar did this too, in the Series 3 XJ-6/12 from 1980-1992, they raised the driving-stop lights and lowered the turn signals.

It was a costly modification since I had to pay for molds and color testing, but the end result is very elegant. I would not go back to the stock setup.

 

TilleyJon,

this is the Brake Lights switch I get at eBay, also sold by Rock Auto, and the part number at Rock Auto is on the title of the image

 

That's a heck of a nice mod you did on those tail lights!
I would image casting your own lens is a bit expensive.

Ever thought of selling this conversion as a kit? Maybe recoup some of your cost?
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clubairth1,

the lenses were expensive to reproduce and nobody wants to pay the cost, except the Registrar of the International Jaguar S type Register purchased a pair. He liked it too.

here's another sample of the three options that S type owners have. Note that the tail lights in the S type are the same tail lights as in the MK-X, the 420-G, and the 420.
By the way, if you have a S type, you can raise the Driving / Stop Lights the same way by using two Red lenses.

The European, Australian, & Canadian cars have the Top Lens in Amber, the bottom Lens in Red.

The American cars have both Lenses in Red.

I modified mine to have the Top Lens in Red, (Driving and Stop lights), and the bottom Lens in Amber, (Turn signals).

it looks like a Bentley or Rolls Royce of the same period, which used the same tail lights as the Jaguar MK-X, 420-G, S type, and 420.

And to repeat, Jaguar did the same in the Series 3 XJ-6, they raised the Driving and Stop lights (Red upper sections), and lowered the Turn Signals, (Third amber section). (last picture).

the color differences seen in the pictures is that they were taken at different times with different lighting conditions, the Amber color is darker than it looks in the below pictures. The best representation of the real color is the picture of the tail light assembly that I posted in post #14 above.