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Brake Warning Light. On then off and then on!


jbud
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Hi

I've read a lot about the brake warning light but can't solve my problem. I have a 1983 Series 3. There is not test button, just the rectangular brake light in the center dashboard.   Basically the light turns on when the ignition is turned on (first two clicks). It goes off when the engine is cranking (which is when I thought it was supposed to go on) and then remains on after engine has started, key goes back one click..

Perhaps the wrong ignition wire to the relay?  Thoughts!

Thanks

J

Edited by jbud
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I have no hands-on experience, but this extract from the Workshop manual may help. Note that the lamp may be a button that acts as a test switch.
I note your USA location, but don't have a section relating to USA vehicles (if such a section exists).

Regards.

S3-Brake-Warning-light-Wkshop-description.gif

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Thanks for this. I'll read and digest.  Despite being in the USA, the S3 is a RHD one I imported many years ago when I moved to this country from the UK..   My understanding is that on the late S3's the only switch in the circuit is the pressure differential switch with a dual brake system and that the travel and vacuum switches weren't installed....but I'll check again.  Also there's no test switch, just a rectangular Brake light. I disconnected the pressure diff switch to open the circuit (light should have gone off) but it remained illuminated indicating a ground situation somewhere else in the circuit.  I'll check to see if the other switches exist or not and if so whether they're faulty.

The joys of S3 ownership....I love them!

Thanks.

J

 

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It should go out, I'm afraid it's time to chase the circuit, as it suggests a fault with the system. 

Don't assume it's electrics, it could be a brake failure. A leaking pipe can trigger the PDWA switch.

For electrics:

It could be the relay, the vacuum or the Pdwa in your system, (same as mine).

The test procedure in Davids excerpt still applies.

Start at the vacuum, easiest to access, then pdwa, then relay. 

If all good, then you might have a chafed wire.

 

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If it’s coming on with the ignition switch at II but not in the starting position, it’s likely to be a wiring fault between the ignition switch and the big silver relay that does the bulb test on engine start.  Someone may have connected the trigger wire (a smaller diameter white wire with red trace) to the wrong ignition switch terminal.

Otherwise, you need to do a continuity test on the other switches in the warning system to see which has a closed circuit - it could be detecting a failure in the related subsystem (pressure differential warning assembly has shifted, or servo vacuum is not holding), or a switch has failed closed.

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Snagger

Do you know which relay terminal the ignition wire should be connected to.   The light does come with the ignition switch but not in the starting position so I am starting with a wiring fault assumption. The brakes work really well with no softness etc.  I only realized that this light existed when I replaced the fuse that is connected to the relay (and I've had the care for 8+ years!).

 

Thanks

J

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I had to sort one on a similar vehicle many years ago.  The problem with this vehicle was that it had started life as petrol and been fitted with a diesel engine, with the petrol wiring beng retained.

 

I seem to remember working out that a relay was used to provide power to the warning light when the key was turned, the problem being that the diesel turned off much of the electrics when the key was turned.

 

The problem is that Rover were reluctant to provide wiring diagrams for anything after about 1972.  I seem to remember finding what I needed in the lightweight diagram which was a bit curius as they were all petrol.

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22 hours ago, jbud said:

Snagger

Do you know which relay terminal the ignition wire should be connected to.   The light does come with the ignition switch but not in the starting position so I am starting with a wiring fault assumption. The brakes work really well with no softness etc.  I only realized that this light existed when I replaced the fuse that is connected to the relay (and I've had the care for 8+ years!).

 

Thanks

J

I don’t know which terminal it is by number or position, but it should be on the same terminal as the thick white and red wire to the starter solenoid - that’s why the relay trigger wire is coloured that way; it matches the starter circuit.

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That diagram is for the type of warning lamp with press-to-test, the circuit connected to the white ignition circuits, not the solid mounted lamp with automatic self-test with the test trigger to the ignition switch.

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Hi

I figured it out.  The red/white wire to the BRAKE warning light relay was off the wrong spade on the ignition switch.  You may be able to see from the pic attached but the two red/white wires were coming off two different spades.  Figured out which was the starter spade, connected the other and all works perfectly.

Many thanks to this community.

J

IMG_0605.jpeg

Edited by jbud
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On 7/7/2020 at 6:36 AM, Snagger said:

If it’s coming on with the ignition switch at II but not in the starting position, it’s likely to be a wiring fault between the ignition switch and the big silver relay that does the bulb test on engine start.  Someone may have connected the trigger wire (a smaller diameter white wire with red trace) to the wrong ignition switch terminal.

Otherwise, you need to do a continuity test on the other switches in the warning system to see which has a closed circuit - it could be detecting a failure in the related subsystem (pressure differential warning assembly has shifted, or servo vacuum is not holding), or a switch has failed closed.

I stand corrected. There's none in the usual places, am I also wrong wrt to not seeing a late S3 wiring diagram?

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The Haynes book has the various different ages of SIII wiring diagrams, and they probably came from LR.

The main circuit of the late warning system would be run from the white circuits of the fuse box, so that is probably where the mistake has occurred, someone mixing up the feed to the system and the self test trigger.

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10 hours ago, jbud said:

Hi

I figured it out.  The red/white wire to the BRAKE warning light relay was off the wrong spade on the ignition switch.  You may be able to see from the pic attached but the two red/white wires were coming off two different spades.  Figured out which was the starter spade, connected the other and all works perfectly.

Many thanks to this community.

J

IMG_0605.jpeg

Glad to help and that it was a simple, zero cost fix.

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  • 1 year later...

Sorry to be getting in on this post late.  I have an 83 diesel 88, S3.  I see from a cicuit diagram and mention in the above post that there is a brake check relay -  where is it located?   I am replacing my starter switch and with the dash pulled out I find the voltage stabiliser and what I think is the flasher unit,  but not something I would call a relay.  Help appreciated.  The check light never has worked as described in the manual.   

Jim

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It should be behind the instruments.  Look for a fairly large steel cased relay with black/white stripe wires and a single white with red stripe wire (if yours is the type tested when the starter is on, rather than press-to-test). 

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On 7/17/2021 at 1:07 AM, 83county88 said:

Sorry to be getting in on this post late.  I have an 83 diesel 88, S3.  I see from a cicuit diagram and mention in the above post that there is a brake check relay -  where is it located?   I am replacing my starter switch and with the dash pulled out I find the voltage stabiliser and what I think is the flasher unit,  but not something I would call a relay.  Help appreciated.  The check light never has worked as described in the manual.   

Jim

It is usually located in the centre of the dash. There is a housing with the Hazard Warning and Fog Lamp switch and warning lights. The relay should be situated behind the two piece panel/housing. At least that's where mine is in my '84 2.25 petrol 88". 

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  • 8 months later...
On 7/7/2020 at 3:28 AM, David Sparkes said:

I have no hands-on experience, but this extract from the Workshop manual may help. Note that the lamp may be a button that acts as a test switch.
I note your USA location, but don't have a section relating to USA vehicles (if such a section exists).

Regards.

S3-Brake-Warning-light-Wkshop-description.gif

The brake warning light works as follows:

1. When the ignition is turned on the light should be ON because the vacuum switch is on since there is no vacuum before the engine is turned on.

2. When the engine is started the light should go Off because the vacuum switch turns off when vaccum is present.

3. If the light remains ON, It could be caused by the PDWA switch. The switch is ON if the piston inside is dislocated because it has stopped a leakage in the system. Dislocation of the piston can also occur during  bleeding the brake system. It is important to open the bleeder screws gently to avoid this.

4. If the light turns ON when the brake pedal is activated the travel switch has turnd ON indicating excess brake travel. This is caused by brake shoe wear and should be fixed by adjusting or replacing the brake shoes.

Fault diagnosis.

1. If the light does not turn ON when the ignition is turned on, the light bulb can be tested using the dash mounted test switch. If it does not turn ON, the bulb probably needs to be replaced. 

2. If the light is constantly ON it can be caused by any of the switches being ON. The correct method to find the switch which is ON is to disconnect them one by one until the brake warning light goes Off.                  The procedure described in section 6b in the manual above where the leads are  connected using a LUCAS male connector will not cause the light to go Off. On the contrary it will make it turn ON.

I hope this is helpfull to understand the system.

Best regards 

Torben 

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