Brake Light Switch (short life)

[svenedin]

This has been discussed many times before but I am not sure this particular solution has been suggested.

Many people will be familiar with the currently available brake light switches failing after a short time of roughly 1 to 3 years. This compares to decades for the original switches. The symptoms of the switch starting to fail are that the brake lights are dim with light pedal pressure only becoming bright with firm brake pressure.

Today somebody beeped me as I stopped to turn right. I dismissed this as an inpatient driver at the time but then asked somebody to stand behind the car whilst I pushed the brake pedal. Sure enough dim brake lights with light pedal pressure only getting bright with firm pedal pressure. We tested in the dark so actually the brake lights might have been too dim to see in bright sunshine.

I sighed as I thought I would have to replace the switch. It isn't so hard to change the switch but the brakes may need bleeding afterwards and that is tedious. I only bled the brakes a week or so ago!

Then I remembered I had some LED combined stop/tail light bulbs. I fitted these and instantly, I have bright brake lights with light pedal pressure.

I believe that one theory of why the brake switch fails is that it carries quite a large current with 2x incandescent Stop bulbs of 21w. With LED bulbs this current must be greatly reduced. Might this significantly extend the life of the switch?

Stephen

[Bill_qaz]

Another solution is to use the switch to operate a relay (very low load) then the relay is taking the bulb load rather than the switch

[svenedin]

Another solution is to use the switch to operate a relay (very low load) then the relay is taking the bulb load rather than the switch

Thank you. I will also have a hunt for a NOS switch. The original part number was 8H1894 (Lucar connectors) in AKD 3541 but the Moss diagram shows C16072A

Does anybody know what the thread is on this switch? I don't have a spare to check it.


Stephen

[geoberni]

According to the parts manual, the original Lucar/Spade terminals was Pt no 3H 1894.

The latter Screw Terminal (after car 990290, the start of S5) was 2A 5740, subsequently replaced by 13H 1731.

This link to Bull Motive Mini Spares says the C16072A was a return to Spade terminals (1963-76)
https://www.minispares.net/product/swit ... 740/2A5740

[Bill_qaz]

20250417_095954.jpg (561.97 KiB) Viewed 5963 times

[mike1864]

I'd be wary of using a demonstrably naff switch to drive a relay.
Its contacts are already exhibiting a variable resistance, when it should be either zero ohms or infinite ohms.
So something is on its way out, either mechanically or chemically.
Its current (ie today's!) resistance may be low enough to work LEDs.
But it's unlikely to get better, only worse.
As I've mentioned elsewhere, I'd also be wary of LEDs anyway, when a coloured lens is involved. Unless the spot wavelength of the LED's spectrum matches the colorimetry passband of the red plastic, the combination could be far dimmer than the standard setup. (And a white LED won't help, as it actually generates three spot wavelength colours).

[Bill_qaz]

Mike, I was suggesting a relay with a replacement switch to increase it life span not to cure the defective switch

[mike1864]

Understood, Bill.
But the replacement switch mustn't be of the same type that claims to be happy with 3.5 Amps, but rapidly deteriorates (with either time or current) to pass only a few milliAmps.
The bottom line, of course, is why in 2025 it's so difficult to manufacture a switch to a 1948 specification!

[svenedin]

I have just been down to ESM where they did the tracking and headlight beam adjusting for me. Whilst there they replaced the brake switch.

ESM told me that they had taken the modern switches apart and they are quite different internally to the old ones. The new ones have a washer that moves with the fluid pressure and makes the contact. The old ones work differently. The new ones arc and develop high resistance then fail completely. We all agreed that it is a complete puzzle as to why switches cannot be made to the original specifications which lasted for decades.

Stephen

[geoberni]

What hope is there of having any confidence when this identical image, frequently with different retailer's watermark emblazoned, is used to advertise a Brake Light Switch as suitable for different classic British marques, with a price range of £7.42 to £29.99

BLS.JPG (29.5 KiB) Viewed 5907 times

[svenedin]

What hope is there of having any confidence when this identical image, frequently with different retailer's watermark emblazoned, is used to advertise a Brake Light Switch as suitable for different classic British marques, with a price range of £7.42 to £29.99
BLS.JPG

All the same junk!

Stephen

[svenedin]

20250417_095954.jpg

This is very helpful thank you Bill. I have managed to find a Bosch one and a NOS old Intermotor one. Neither of them appears to be the same as all the bad modern ones

Stephen

[firedrake1942]

I bought two NOS (screw type) brake light switches from Club Spares at the last open day in Derby. As I recall there were loads of them still in BMC boxes. May be worth giving them a ring. Hopefully there is now some system in the chaotic storage of spares.

[svenedin]

I bought two NOS (screw type) brake light switches from Club Spares at the last open day in Derby. As I recall there were loads of them still in BMC boxes. May be worth giving them a ring. Hopefully there is now some system in the chaotic storage of spares.

Thanks for the tip but I don't think the club has anybody in charge of Minor 1000 spares now that Bryan has moved to MM and Series 2 only. I have e-mailed the address in the magazine spares advert anyway and we'll see what happens. The club have been trying to recruit somebody to do the spares for ages but nobody was able to take this on.

Stephen

[Bill_qaz]

Understood, Bill.
But the replacement switch mustn't be of the same type that claims to be happy with 3.5 Amps, but rapidly deteriorates (with either time or current) to pass only a few milliAmps.
The bottom line, of course, is why in 2025 it's so difficult to manufacture a switch to a 1948 specification!

If the switch is so bad it won't pass 150-200 MA to operate a relay then they are even worse than I thought.

[svenedin]

My e-mail to club spares ended up going to Bryan who told me there was nobody dealing with the Morris 1000 spares (which I knew already). I said I had been told there were loads of brake light switches at the club open day at Derby. We'll see what he says. I also asked him about the engine mounts. Bryan thought ESM had sorted it out but I told him they haven't.

Stephen

[svenedin]

Bryan from Club Spares has very kindly found a new old stock original Lucas 34542 brake light switch so I am all sorted. If it lasts as long as the original one did in my car I will never need to replace it in my lifetime! The modern one lasted 2 years. I presume it went faulty very recently as it would have been picked up at the MoT test.

Stephen