Ignition warning light coming on under braking?

[mikey_p]

RobP is at Spa at the moment and is experiencing this after about 10 minutes of track time, which I guess would indicate a possible issue with heat.

Basically when under breaking the ignition warning light comes on, and it extinguishes when he lifts off the brake (after 10 minutes of giving the car a good thrashing).

The battery has been tested and is taking a charge.

Any ideas and help would be appreciated.

Cheers,
Mike

[AMG Merc]

How old is the brake fluid?

[mikey_p]

AMG Merc said:

How old is the brake fluid?

Not sure, but the car was serviced very recently. Also if it is the brake fluid would it not be the handbrake light that would come on, as he has had that light flashing on under braking before, which was obviously indicating a low brake fluid level.

[Adrian W]

bet it's the oil pressure switch wire touching the exhaust, burnt through the insulation and making the lamp flicker.

[chippie]

Adrian W said:

bet it's the oil pressure switch wire touching the exhaust, burnt through the insulation and making the lamp flicker.

And that would make the low oil pressure light come on.

[GreenV8S]

Make sure it really is the ignition warning light. The way to test is to rev the engine and switch off. The ignition warning light will usually glow as the engine spins down. (I'm not sure if this test will still work if your warning light is an LED.) If you see the light glow that confirms it's the ignition warning light, otherwise you'll need to do more tests.

I'd have thought that low oil pressure and brake wear/low fluid warnings were both more likely. If it's really the no charge light coming on, I'd guess there's a break between the battery and the alternator under heavy braking, perhaps in the area of the <spit> fusible link.

[mikey_p]

GreenV8S said:

Make sure it really is the ignition warning light. The way to test is to rev the engine and switch off. The ignition warning light will usually glow as the engine spins down. (I'm not sure if this test will still work if your warning light is an LED.) If you see the light glow that confirms it's the ignition warning light, otherwise you'll need to do more tests.

I'd have thought that low oil pressure and brake wear/low fluid warnings were both more likely. If it's really the no charge light coming on, I'd guess there's a break between the battery and the alternator under heavy braking, perhaps in the area of the <spit> fusible link.

I'm sorry I don't understand. What do you mean "to make sure it is the ignition warning light"? As it is the ignition warning light that is turning on (as in the one that has a battery symbol on it).

And surely if it is low brake fluid or low oil pressure, then the handbrake/brake fluid level warning light, or the oil pressure light would illuminate.

The alternator has been considered, but i'm not sure if it has been checked, and just for information purposes, the front turbo has been removed and replaced very recently.

[GreenV8S]

mikey_p said:

I'm sorry I don't understand. What do you mean "to make sure it is the ignition warning light"? As it is the ignition warning light that is turning on (as in the one that has a battery symbol on it).

What I mean is, I don't know about the Noble lights specifically but the oil pressure and no charge warning lights are often physically close together and look similar. The only time you'll usually see them they will tend to come on together so it would be easy (a) to be mistaken about which lamp actually came on under braking, or (b) have a car with them wired in the wrong way round and not realize.

[mikey_p]

GreenV8S said:

mikey_p said:

I'm sorry I don't understand. What do you mean "to make sure it is the ignition warning light"? As it is the ignition warning light that is turning on (as in the one that has a battery symbol on it).

What I mean is, I don't know about the Noble lights specifically but the oil pressure and no charge warning lights are often physically close together and look similar. The only time you'll usually see them they will tend to come on together so it would be easy (a) to be mistaken about which lamp actually came on under braking, or (b) have a car with them wired in the wrong way round and not realize.

I did think about that as I seem to remember that it was the 3R that had the brake fluid low light coming on under braking, and now he is driving the M400.

It is however easy to tell which light is coming on due to the layout of the lights on the dash, and there are two lights in between the ignition warning light, and the low brake fluid level (and driving a Noble keeps part of your senses constantly tuned into dashboard lights and readings, and odd noises ).

[GreenV8S]

mikey_p said:

odd noises ).

Yes, I suspect the 'warning lights wired back to front' thing is mainly a TVR foible but having seen them wired the wrong way round I don't trust them now on any car until I've made sure.

[AMG Merc]

mikey_p said:

AMG Merc said:

How old is the brake fluid?

Not sure, but the car was serviced very recently. Also if it is the brake fluid would it not be the handbrake light that would come on, as he has had that light flashing on under braking before, which was obviously indicating a low brake fluid level.

I meant that if the fluid is old it could have got water into it (become abscorbic (is that the correct term?)) and so would boil faster - hence the warning light may go on sooner and only after hard braking.

Not sure the handbrake uses fluid - I mean isn't it a separate system - drums only? If the handbrake light was flashing then it could be the handbrake switch (under the handbrake) that's faulty.

[JLSELAN]

AMG Merc said:

mikey_p said:

AMG Merc said:

How old is the brake fluid?

Not sure, but the car was serviced very recently. Also if it is the brake fluid would it not be the handbrake light that would come on, as he has had that light flashing on under braking before, which was obviously indicating a low brake fluid level.

I meant that if the fluid is old it could have got water into it (become abscorbic (is that the correct term?)) and so would boil faster - hence the warning light may go on sooner and only after hard braking.

Not sure the handbrake uses fluid - I mean isn't it a separate system - drums only? If the handbrake light was flashing then it could be the handbrake switch (under the handbrake) that's faulty.

You're right, the handbrake is a mechanical system that is completely independent of the hydraulic brake system. However it is very common for manufacturers to use the "handbrake light" in a dual mode--to indicate both that the handbrake is engaged and that the brake fluid is low. Also, in general, boiling brake fluid is a local condition (at the calibers) that does not affect brake fluid level, so boiling would not be something that would necessarily turn on the brake warning light--but you would definitely know you have a problem because braking effectiveness would be drastically reduced!

[NobleGuy]

You guys seem to be psychic - I was about to post about a flickering brake warning light after I read this one. Only happened once under heavy braking (after a few roundabouts of the same) and hasn't recurred since. Will check my fluid today - thanks guys .

[mikey_p]

AMG Merc said:

mikey_p said:

AMG Merc said:

How old is the brake fluid?

Not sure, but the car was serviced very recently. Also if it is the brake fluid would it not be the handbrake light that would come on, as he has had that light flashing on under braking before, which was obviously indicating a low brake fluid level.

I meant that if the fluid is old it could have got water into it (become abscorbic (is that the correct term?)) and so would boil faster - hence the warning light may go on sooner and only after hard braking.

Not sure the handbrake uses fluid - I mean isn't it a separate system - drums only? If the handbrake light was flashing then it could be the handbrake switch (under the handbrake) that's faulty.

As JLSELAN mentioned, in the Noble the handbrake light is also the warning light for low brake fluid level (it says in the manual, and has happened before to RobP). That also only seemed to occur under heavy braking. It could be a possibility that the warning lights have been wired in the wrong way, however when the car is started (or stalled, as I know) the ignition light comes on, so appears to be working effectively. As with the handbrake light, when the handbrake is applied, the correct light comes on, whether the warning part of the system is wired up differently though I do not know.

I'll give Rob a ring and see if they have found anything else, as he has another day at Spa today, and then a few days touring France so I really don't want the car to give up on him.

Cheers for the replies so far though guys .

[RobP]

Adrian W said:

bet it's the oil pressure switch wire touching the exhaust, burnt through the insulation and making the lamp flicker.

Prize (strawberry milkshake) goes to Adrian for nearly getting the right answer.
As with many of these electrical things it's only when they fail completely that you can find the problem.. Just as I was supposed to be leaving the circuit fuel-pump didn't prime and so car wouldn't start. After a few Basil Fawltey moments ( birch twig and threats to car) it transpired that the fuel pump wiring was being fried by the front turbo. Presumably when it all got very was hot after 10 mins or so on track, movement under braking caused some sort of short - hence ignition light flickering). Fortunately, Stuart Faulds (from Faulds Motorsports) was on hand and rewired the whole thing from pump through relay to battery (routing the wire well away from turbo). This was done in the car-park at 6.30pm in the semi dark and in the rain. So huge thanks to Stuart for getting us going so we could continue our Euro-tour.

[AMG Merc]

RobP said:

This was done in the car-park at 6.30pm in the semi dark and in the rain.

A true PetrolHead!

[RobP]

AMG Merc said:

RobP said:

This was done in the car-park at 6.30pm in the semi dark and in the rain.

A true PetrolHead!

Indeedy.. could almost forgive him for being a Scotsman! Top chap.

[NobleGuy]

mikey_p said:

As JLSELAN mentioned, in the Noble the handbrake light is also the warning light for low brake fluid level (it says in the manual, and has happened before to RobP). That also only seemed to occur under heavy braking.

Was getting that warning light last week (even though the fluid level was OK) - bled the brakes over the weekend and the fluid looked manky. Not had the warning again.