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Discussion Starter · #1 ·
I was under the back of my 73 GTV today and I found a switch fitted into the hydraulic brake line. The switch is screwed into a cylinder about 75mm long and 25mm dia. The wires have been ripped of a long time a go and had been tucked up out of the way by previous owner.

Can anyone tell me what this switch does as I cannot find it on the wiring diagram.

Thanks
 

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Hi Paul

It is a brake light switch,the same as the the brake light switch on the engine firewall under the boosters.
Common modification was to remove the wires so the brake lights stayed off.
If you dont have any brake issues= dont worry about it.
But sometimes air can leak IN to the rear switch,like the front switch,causing air in the brake system.

Robert
 

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Paul,
Welcome to the list and congratulations on buying such a nice GTV.
The cylinder to which you refer is the rear brake proportioning valve and it has, I think, a secondary set of brake light wiring attached to the pressure sensor. If your brake lights work OK, then don't concern yourself as they will be activated from the primary sensor on the firewall where the front hydraulic lines split to each front caliper.
BTW, these proportioning valves do occasionally play up as they fill with brake fluid debris and rust over the years and jam. Paradoxically, the usual symptom is locking rear brakes, the very thing the valve should prevent. They can be rebuilt.
Cheers,
Chris
 

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Discussion Starter · #4 ·
Thanks Gentlemen, I could not work it out because my brake lights were working fine -now I understand.
 

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Can anyone tell me what this switch does as I cannot find it on the wiring diagram.
As has been said, it is one of two brake light switches. The reason there are two switches (wired in parallel) is that in the event of a hydraulic failure in either of the two brake circuits, the brake lights will be activated by the good hydraulic circuit.

To my knowledge, Alfa did not produce specific wiring diagrams for RHD 105s. I recall seeing a RHD user's manual supplement that shows the hydraulic and wiring circuits as a schematic but it does not provide wire colours.
 

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I was also wondering what this switch was. So it's sole purpose is to illuminate the brake light if it senses a problem?
 

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...and the rear brake light switch is attached to the brake pressure limiting valve (the device pictured above). The purpose of this valve is to limit brake hydraulic pressure to the rear brakes (in relation to front brake hydraulic pressure) to prevent rear wheel lockup under hard braking.
Note that this 2nd brake light switch mounted at the rear is unique to RHD cars having floor mounted pedals and tandem brakes.
 

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Interesting, a second brake light switch. So, a fault on this switch could be the cause of my brake lights glowing dimly when the car standing - resulting in a flat battery?

So, short term, I could disconnect (and tape up) the wires on this sensor and the lights will work off the sensor on the bulkhead. Long term - replace the sensor and reconnect.
 
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