My 1978 ls brake fail light is on all the time, l am hoping when I bleed the brakes this light will go out.
Does anyone know what puts this light on.i cannot see any wiring around the master cylinder area and my manual does not mention it.

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1967 Morris mini Deluxe
1968 Buick Riviera
1979 HZ Kingswood
1979 CM Valiant
1982 Jaguar XJ6 series 3
2002 VX HSV
2013 Mazda 6
2018 Gt Mustang

I seem to remember it having something to do with a split brake system, so there must be a sensor somewhere further in the system.

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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)

Should be a sensor on the master. The light will come on with ign but as soon as the car starts will go out as its wired through the alternator light on the dash.

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The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

Earlier cars had a sensor on the brake t piece on the rh side of the subframe maybe check there.

_________________
The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

GMC 227 master cylinder has a fluid level float switch

Where a pressure failure switch was fitted
cut off connector plug , twist wires together and crimp a lucar connector to the wires
connect to one side of the floatswitch cap
connect a wire with lucar connector to the over side of the cap and run this to a earth

Yes good point. I had an Ls with this light and remember now it goes out once the car starts. As suggested I seem to remember sensor at t piece or elsewhere to master as mentioned.

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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)

I think it is a differential pressure switch that turns on the light, when the pressure in one side exceeds the other side it closes the low side and turns on the light.
From memory it was built into the master cylinder. I recall the plug being positioned between the two outlet pipes.

My original master cylinder had no float switch,but the GMC227 M/cylinder does.

I could wire the float switch up to this light,but there must be another switch somewhere that I have missed.
I suspect it's near the brake pressure valve on bulkhead.

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1967 Morris mini Deluxe
1968 Buick Riviera
1979 HZ Kingswood
1979 CM Valiant
1982 Jaguar XJ6 series 3
2002 VX HSV
2013 Mazda 6
2018 Gt Mustang

As morris has said
on the old master cylinder the pressure switch was between the two out lets
GMC227 does not have this , it has a fluid level switch , which replaces the pressure switch
hence the wiring mod
there is no pressure switch any where else that I know of

Its just another warning light to look at as you spear off the road into the trees without any brakes

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Who needs brakes....

Cheers Brad

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During the day I work on English designed cars & on my own time I work on English designed cars....

Yeah Mick your not wrong more distractions.

Hi slacko,I'll have another look around the engine bay tomorrow for the old wiring.
I think the previous owner may have removed this wiring.
The brake fail light wire must be grounded somewhere as the light is always on.
If I cannot find the old wire I will follow the wire back from the light and connect the ground to the float switch.

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1967 Morris mini Deluxe
1968 Buick Riviera
1979 HZ Kingswood
1979 CM Valiant
1982 Jaguar XJ6 series 3
2002 VX HSV
2013 Mazda 6
2018 Gt Mustang

From memory the wiring for the brake fail switch is a separate pair of wires that don't connect to the main harness.
Power from the fusebox to the dash light, earth from the switch on the master cylinder to the light.
Look at the fusebox and see if you can spot a wire running towards the firewall that joins another wire near the master cylinder area.

Really dim memory time... I think they may have been white and white with a trace?[/clutchingatstraws]

The earth wire for brake fail light was permanently grounded,that is why the light was on all the time.
The earth wire for this light was black with white tracer and yes it was separate from the main loom.

I have connected the float switch in the new master cylinder via this earth and light works as it should.

Thanks for all the info.

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1967 Morris mini Deluxe
1968 Buick Riviera
1979 HZ Kingswood
1979 CM Valiant
1982 Jaguar XJ6 series 3
2002 VX HSV
2013 Mazda 6
2018 Gt Mustang