Marlin have supplied me with a hydraulic brake switch and four way T-piece. The T-piece obviously splits the fluid supply for the rear wheels and provides a fluid connection for the brake switch. The switch is open circuit at rest so presumably closed circuit with pressure (the brake!!) applied.
The current IVA spec says:-
The hydraulic system must be fitted with a red warning lamp, sensitive to line pressure and capable of signalling the failure of any part of the hydraulic system as soon as the brake is applied and remaining lit as long as the failure exists (with the ignition switched on). As an alternative, the warning lamp must be sensitive to the reservoir fluid level, providing the reservoir is directly connected to supply the pressure side of the master cylinder when the piston is in the “brakes off” position, so that a failure of either part of a split system would result in a continuous draining of the reservoir fluid when the control is released (see note 2 and 3).
Note 2 says:-
in the case of a conventional split system (with or without vacuum assistance) it will be assumed that a failure will result in the draining of the fluid. It may be necessary to confirm the fluid circuit through the master cylinder by documentary evidence.
I am using the Marlin supplied Master cylinder (from a Ford P100 I believe) and it looks like the one Jason has used. Does that fulfill the "alternative" method as described above and if it does what were you asked for in terms of documentary evidence.
As an option the circuit below should meet the requirement:
It fulfills the lamp testing requirement via the handbrake and the 'red warning lamp, sensitive to line pressure and capable of signalling the failure of any part of the hydraulic system as soon as the brake is applied' requirement via the change over relay. However, I can't help but think it's over complicated on the basis that if I've hit the brake pedal but I've got no brake pressure the warm and damp sensation in my seat followed by a nasty smell would probably alert me to the fact something is wrong...................!!
So prehaps I don't need a brake pedal switch and can rely on just the hydraulic swith for the brake lights and the fluid level switch and handbrake for the warning light. Or alternatively, just use a standard T-piece with no pressure switch for the rear brakes (especially as I've already fitted it....!!) and use a brake pedal swith for the brake lights.
What have you all done - hydraulic switch or brake pedal switch. Is it a simple choice or have I missed something.
Nigel
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