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Brake light switch

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Old May 14th, 2015, 06:52   #1
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Default Brake light switch

I've owned my Amazon for a year and a half, and in that time I've had to replace my brake light switch twice. I could hardly believe it when I tested it this morning and found yet another bad switch!

Was there a bad run of switches? Does anyone else have this problem?

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Old May 14th, 2015, 11:40   #2
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mate, the hydraulic switches are pretty crap and unreliable.. been there myself. here is a link to fix it for good.
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Old May 14th, 2015, 13:07   #3
Ron Kwas
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Your experience with the hydraulic pressure sensing Brake Light Switch is quite common. See:

In short, it's because of the effects of how slowly the pressure comes up in the Braking System, but if you are interested, you can see a failed switch dissection, and all the gory details in my article here:

I recommend (to all owners who still have hydraulic pressure sensing Brake Light Switches in their vintage Volvo, from 444-122 and 1800 models, including RHD) that they check their Brakelight function often, and consider upgrading to a Pedal Position Sensing Switch (PPSS). This brings with it the distinct advantages of Reliable Brake Light function (mechanical switches are reliable. Volvo as well as the entire automotive industry realized their advantages, and changed over to these in the late sixties), plus what I call Early Brake Light function (since contact closes as soon as Brake Pedal is moved from its resting position, way before any hydraulic system pressure is made, this gives more stopping time/distance to the driver following...which might be of particular interest in busy California! I leave it as a mathematical exercise to calculate the additional stopping time/distance at a given speed).

As you can see, I've been on a bit of a mission to get all vintage Volvo owners to make this upgrade to their vehicles for their, and their passenger's additional safety. It's a simple, inexpensive change with major advantages!

Full Disclosure: I have developed and offer retrofit and upgrade kits with which to add PPSS to all models of vintage Volvos. In the most recent effort (which is nearing end of development right now), I developed a kit specifically for the RHD Amazon in collaboration with members of this forum (I will let them out themselves if they so choose). See:

Kit for RHD Amazon will be available very shortly! Switches for all other models are available now. See:

Cheers from Connecticut to California!
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Old May 15th, 2015, 05:02   #4
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I became suspicious when I noticed people slamming on their brakes every time I pulled into a gas station. Sure enough the dang switch failed again.

I'm torn between the desire to keep the car fully stock vs. the frustration of constant switch failure. Surely after 50 years they could figure out how to make a switch last longer than 6 months!

My sweet wife and I are moving to Missouri in a couple of weeks. When we get there I'm going to take the Amazon down for some badly needed repair work. I may just put the pedal switch mod in....

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Old May 15th, 2015, 10:00   #5
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I really like the principle of the other type of brake light switch, but I would like to consider the older type because I don't think they're as bad as. Yes, they do have significant reports of early failure and I agree that the newer version with a switch on the brake pedal has obvious benefits of the brake lights coming on much earlier.

However, I feel quite sure that the actual reason for early failure of replacement switches are not to do with the switches themselves, even though they are quite flimsy! My thoughts are based on the amount of current running through the switch as follows: Firstly, when I have towed without a relay in the system, the switch quickly burnt out. The other thing is this: those back light units deteriorate quickly and corrosion builds up around the bulb holders, connectors and earth connectors, so the current required to make the bulb light is high. As well, the wires fray, so if there's a short, the current is extremely high.

A good session back there cleaning up all the connectors, earths and bulb holders together with a fresh set of bulbs will soon brighten things up back there. That leads onto the very well discussed thing on this forum about re-painting the rear light reflectors or covering them in high reflective aluminium tape...

ALL the current for the brake lights go through that tiny little switch - 2 x 21w bulbs. Add a trailer and/or an extra brake light.... You see where I'm going. It's a flimsy switch. As such a really simple upgrade which will significantly increase the longevity of it would be to add a simple relay straight off of the fuse box with it's own fuse would ensure as much current as possible will go back to your brake lights AND the only current running across the switch would be that required to activate the little switch in the relay.

This is a well used modification in the air-cooled VW world which has the same flimsy brake light switch.

All said, none of this is a good as a switch down on the pedal!
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Last edited by swedishandgerman; May 15th, 2015 at 10:56.
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Old May 15th, 2015, 14:22   #6
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As I found after dissecting a virtually brand new switch that failed, there was no snap-action or wiping action with that simple design of the contacts...that, combined with how slow they close because of the slowly rising pressure is THE major factor why these switches don't general, switch contacts are designed with spring mechanisms to provide fast-make/fast-break in order to 1. cut through surface oxidation to assure current flow, and 2. prevent prolonged arcing and the resulting heat...unfortunately not here, because the diaphragm simply follows the system pressure...not to mention the inrush current of incandescent lamps can easily be double the steady-state when you say 2 X21W (3.5A, scale that up even more when adding trailer lights!), that's only what current settles down to after an inrush shot way more then that...all these factors combine to force the switch to operate in a worse than worse-case scenario, which leads to an early failure...

I do have to disagree with your suggestion that corrosion somehow increases the current...It Cannot! Any poor connection in series with a load in a simple circuit as this** acts to increase circuit R, this drops Voltage available to Lamp and thereby decreases I (which decreases brightness, reference: Ohms Law I=V/R).

** In complex circuits, where the amount of energy pulled from the power source is constant due to some controlling circuit assuring that voltage being supplied to load and therefore current through load are constant, total circuit current would be increased by a series resistance (ie corrosion), but this does not apply in the case of a simple circuit, consisting of a power source, switch, and lamp.


"Surely after 50 years they could figure out how to make a switch last longer than 6 months!" I doubt any manufacturer is interested in spending one dime in doing any continuing engineering or improvement on these switches at this point. There is just no return on that investment! are happy selling you replacements of that terrible (oops! I almost said POS!) switch 'till the cows come home...

"I'm torn between the desire to keep the car fully stock" if you mean stock for year of manufacture of an earlier chassis, adding the bracket wouldn't be...BUT, stock, as what the factory produced, it absolutely would be! ...because the bracket with PPSS will absolutely look the same as the later chassis which also had it! A concourse judge making an inspection of the engine compartment would not see much difference!

VOC member Amazonauto had similar concerns of originality (reference thread: ...I invite him to chime in here with his impressions...but here is the finished appearance of his efforts...absolutely stock! go along with his spotless stock engine compartment! Pic used with permission:

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Old May 16th, 2015, 16:08   #7
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Inconceivable to me that there is not a high-quality exact replacement available for the early switch from outside the automotive supply chain...

I haven't bothered to track one down as my Amazon is on only the second one IN IT'S LIFE,
And I have still have several NOS ones on the shelf, and a couple of the later setups as well.
Would be happy to send a switch/bracket, FOR FREE, with free shipping to whoever lives the furthest from northern New England.
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Old Nov 30th, 2015, 15:28   #8
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Default Amazon Brake Light Switch

Hi I am new to this forum but don't actually own an Amazon (although a 122 or 123 is on my wish list) but my reason for joining is the issue with this Lucas Brake Light Switch.

I am a member of the Mini Cooper Register and the Morris Minor Owners Club. Both clubs are interested in the failure of these after market switches and indeed failures with other parts that are manufactured in the far east. Concerned individuals in both clubs are trying to illicit help in bringing these issues into a public domain to achieve recognition from the many specialist suppliers that they need to smarten up their act when procuring classic car parts. We would like to use your detailed article on the issue to illustrate just how serious this problem is. Is there anyone that can give that permission and indeed are there any like minded individuals they can lend a hand.

Currently I have contacted the Federation of British Historic Vehicle Clubs and the Parliamentary Committee for classic cars, neither has had the common courtesy to reply and we are now lobbying sympathetic journalists in the classic press. There are many serious issues with safety critical car parts that one day is going to end in horrific if not fatal accidents, we are determined not to let this matter rest!

Please re-post any answer/communication here as I am at the moment unfamiliar with your forum.

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Old Dec 1st, 2015, 01:10   #9
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Welcome to this Forum.

Poor Hydraulic Brake Light Switch function issue can be explained by the interaction of three separate factors:
1. Common practice of sensing hydraulic brakeline pressure (which was typical for many manufacturers in its day) This means that rate of pressure rise is slow (that's because we are taught to decelerate and apply the brakes slowly...and that also means the contact will close slowly (see: 2), if we jab on the brakepedal while driving (panic-stop!), or in testing in the driveway when vehicle isn't moving, they will typically work fine, but in a real-world driving situation if we were to apply pedal pressure like that, (see: 3) we would put our passengers into the seatbelts, and few people will want to ride with us.)
2. Switch Design Construction. All failed switches I've ever inspected or performed a post-mortem on, the closing contact was essentially under direct control of the pressure and without any fast-make-fast-break mechanism in sight. This is common practice in electrical industry switches and it serves to slam the contacts closed (typically accompanied by a click or snap of the mechanism), preventing arcing/carbonization during slow closing, and cutting through what little arcing and carbonization does occur, to assure contact. In Hydraulic Brake Light Switches, such a mechanism, which would accommodate the slow pressure rise, is conspicuously absent. I doubt any manufacturer will want to incur costs now, of redesigning this ancient technology for the market of selling a limited number of replacement...little cost/benefit!
3. The Driver Factor. People who apply their brakes with a quick jab, then back off and apply gently rising pressure will experience switch failure less. I "Brake like an Animal" when I'm alone, and would cause even a hydraulic switch to function pretty well, but if I'm taking my grandma to buy cheese danish, I doubt my hydraulically switched Brake Light were working so good.

The motor vehicle industry also saw the light, and unanimously went away from Hydraulic Pressure Sensing Switches (HPSS) and to Pedal Position Sensing Switches (PPSS) in the late sixties, in part recognizing the weaknesses (slow activation of Brake Lights being only one of them!), and for all the benefits. I expect that maybe even Mini and Minors made after that time period were equipped with this advice would be to upgrade ALL earlier vehicles with these PPSS!...don't mess with the HPSS, and don't expect manufacturers to design a better replacement's kindof like asking them to design a leather strap Friction Brake...we're waaaayyy past that!

If you are referring to this "detailed article" (, you are welcome to reference it to whomever you like if you give credit to the source and author.

Cheers from Connecticut!
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Old Dec 1st, 2015, 08:49   #10
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A very detailed and informative reply from Ron as usual, but what I believe davybl was wanting to highlight is the large number of poor quality replacements on the market for various components. The brake light switch is just one of them and as unsuitable a design as this was, the original ones did last very well unlike these cheap copies.
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