Brake lights permanently on?
Discussion
So for about two weeks I've had a problem. My cruise control has not been working. And I've had cars flashing at me when driving home later at night. I assumed that it was an older french car so luxuries like cruise control were expected to not work. I was pretty sure it wasn't the clock spring as when I set it to speed limiter the buttons worked. The flashing I put down to silly other drivers behind me.
However today I have solved the cruise problem. Driving to the tip I decided to turn the lights off. As odd as this sounds I only drive my car early when it's dark or late when it's dark ususally so the lights are never off. But turning the lights off made the cruise start working! A true eureka moment. As soon as the lights are back on no cruise.
So I've checked and the brake lights are on all the time if the main lights are on. The cruise is knocked off by the brakes so I assume it uses the lights (or peddle switch) as a demobiliser for the cruise. Some sort of electrical signal is at play.
My first thing I'll check is the switch. Basically take it off and see if the wiring looks dodgy. I don't have the wiring diagram so can't really test it by backprobing. But I will have a DMM on it and see if my playing with the switch adjusts any voltage. If that doesn't fix it I'll start looking for earth problems. But that will be a pain as I don't have a test light or anything longer than fluke test leads. Plus if the wiring is dodgy the roof goes down on the car so getting access might be a drama. I suppose if I can work out it's playing up I can just bypass the ground.
But... is there anything else you more mechanically genius types can suggest I look at? Is there anything else obvious I should be doing?
I do sort of wonder if a dodgy bulb (think it's dual filament and could be touching) could ignite the brake lights and the cruise might be controlled by a closed circuit on the light. Is that possible? If so I'll buy a bulb and swap them. I can't see it being the switch as this only happens when I have the main lights on.
Just really looking for what others would be doing to try and fix this. Many thanks.
However today I have solved the cruise problem. Driving to the tip I decided to turn the lights off. As odd as this sounds I only drive my car early when it's dark or late when it's dark ususally so the lights are never off. But turning the lights off made the cruise start working! A true eureka moment. As soon as the lights are back on no cruise.
So I've checked and the brake lights are on all the time if the main lights are on. The cruise is knocked off by the brakes so I assume it uses the lights (or peddle switch) as a demobiliser for the cruise. Some sort of electrical signal is at play.
My first thing I'll check is the switch. Basically take it off and see if the wiring looks dodgy. I don't have the wiring diagram so can't really test it by backprobing. But I will have a DMM on it and see if my playing with the switch adjusts any voltage. If that doesn't fix it I'll start looking for earth problems. But that will be a pain as I don't have a test light or anything longer than fluke test leads. Plus if the wiring is dodgy the roof goes down on the car so getting access might be a drama. I suppose if I can work out it's playing up I can just bypass the ground.
But... is there anything else you more mechanically genius types can suggest I look at? Is there anything else obvious I should be doing?
I do sort of wonder if a dodgy bulb (think it's dual filament and could be touching) could ignite the brake lights and the cruise might be controlled by a closed circuit on the light. Is that possible? If so I'll buy a bulb and swap them. I can't see it being the switch as this only happens when I have the main lights on.
Just really looking for what others would be doing to try and fix this. Many thanks.
I think you've hit the nail on the head - it's normal for CC to disengage when the brakes are engaged and it seems that yours is controlled by the brake light circuit, and in your case this is being back fed from the side lamps.
I would start with the bulbs, and their installation in the bulb holder.
Do you have separately working brake and tail lights controlled by the brake switch and side light switch? If not, it may be that somebody has installed the wrong bulbs or the right bulbs the wrong way round such that the contacts in the bulb short across both contacts on the bulb holder. It may only need one side to be wrong to cause these effects. It could also be a wiring fault. It could also be a faulty earth at the lamp cluster - in this case the lamps might not work at all or might brighten and dim in combination as power is applied to different circuits.
I would start with the bulbs, and their installation in the bulb holder.
Do you have separately working brake and tail lights controlled by the brake switch and side light switch? If not, it may be that somebody has installed the wrong bulbs or the right bulbs the wrong way round such that the contacts in the bulb short across both contacts on the bulb holder. It may only need one side to be wrong to cause these effects. It could also be a wiring fault. It could also be a faulty earth at the lamp cluster - in this case the lamps might not work at all or might brighten and dim in combination as power is applied to different circuits.
Oldandslow said:
Pericoloso said:
Brake light switch is stuck ,got to be.
I thought that from the description but brake lights only on when side/headlights turned on so a back feed from an adjacent tail light sounds like a good starting place.Pericoloso said:
Brake light switch is stuck ,got to be.
This was my first idea. But if the switch was stuck then surely the brake light would be on when the normal lights were not as well? They are connected somehow.
It's more complicated than the switch. As if the switch was the only issue the brake lights would always be on.
Sitting here thinking about it I reckon the the voltage to the brake lights are monitored which disables cruise. I have no wiring diagram of experience of cruise so might be talking jibberish. So either I'm likely looking at the light and brake lights shorting due to rubbing wires coming into contact, or I'm looking as a dodgy bulb which is allowing the circuit to become energised. That could be the bulb or the contacts which are connecting the bulb. I'll have a good look at see if I can work it out.
I am starting to have my suspicions... This all started when I had my MOT or shortly after it. I say shortly after as I drove it there in the day, and left it until I went back to work. The MOT place will change a bulb for free for me rather than failing my car. They are great guys. So I reckon the appentice might have changed a bulb. I shall get to the bottom of this tomorrow with some luck.
I'll post back if I find the solution and if not with what testing I've done and how I'm still none the wiser.
Cheers for all the comments guys.
rigga said:
Everyone is mentioning bulbs, the wrong one fitted etc, pretty sure the OP would know if any had been replaced recently ...... no mention of that so far.
O.P. said: I am starting to have my suspicions... This all started when I had my MOT or shortly after it. I say shortly after as I drove it there in the day, and left it until I went back to work. The MOT place will change a bulb for free for me rather than failing my car. They are great guys. So I reckon the appentice might have changed a bulb. I shall get to the bottom of this tomorrow with some luck.rigga said:
Everyone is mentioning bulbs, the wrong one fitted etc, pretty sure the OP would know if any had been replaced recently ...... no mention of that so far.
If it's corrosion in the bulb holder, then it will be fine when a bulbs fitted and then much later will corrode to a point where you get problems.Athlon said:
rigga said:
Everyone is mentioning bulbs, the wrong one fitted etc, pretty sure the OP would know if any had been replaced recently ...... no mention of that so far.
O.P. said: I am starting to have my suspicions... This all started when I had my MOT or shortly after it. I say shortly after as I drove it there in the day, and left it until I went back to work. The MOT place will change a bulb for free for me rather than failing my car. They are great guys. So I reckon the appentice might have changed a bulb. I shall get to the bottom of this tomorrow with some luck.I said on here I had a suspicion about the bulb. But armed with 3 DMM's and some wiring diagrams I forgot about that. Suffice to say panels were removed. Continuity was checked. The testing went on and on. And then I took the bulb out...
So I'm the biggest plonker in town. Rather than the twin filament bulb it was single! So the problem has been solved for less than 40 pence from carparts4less. Atm to stop my brake lights being permanently on I have taken the bulb out and am running with just one rear light. That isn't a massive problem as I'm not really using the car atm.
In my defence this car has been hitting me with multiple things at once. Last week I changed the battery as it stopped working. Usually only after a long drive. Thought it was a heatsink problem with the starter motor and wasted time looking at that. Then just checked the battery and realised it was toast. Then this. It also has a coolant leak somewhere. I'll look at that when I'm back from holiday.
Just when I finished working that out today my Mum called me saying her car wouldn't open with both keys. She didn't realise you could use the actual key to open it so drove around to have a look. She must believe I'm far more competent than I really am. Voltage in her battery was under 4V! I'm wondering if I'm messed up her battery when she let me jump start my car. I'll get her a new battery tomorrow and hope for the best. I would try and jump/trickle charge it but I'm fairly sure that as the battery has got that low it will be toast.
So I'm the biggest plonker in town. Rather than the twin filament bulb it was single! So the problem has been solved for less than 40 pence from carparts4less. Atm to stop my brake lights being permanently on I have taken the bulb out and am running with just one rear light. That isn't a massive problem as I'm not really using the car atm.
In my defence this car has been hitting me with multiple things at once. Last week I changed the battery as it stopped working. Usually only after a long drive. Thought it was a heatsink problem with the starter motor and wasted time looking at that. Then just checked the battery and realised it was toast. Then this. It also has a coolant leak somewhere. I'll look at that when I'm back from holiday.
Just when I finished working that out today my Mum called me saying her car wouldn't open with both keys. She didn't realise you could use the actual key to open it so drove around to have a look. She must believe I'm far more competent than I really am. Voltage in her battery was under 4V! I'm wondering if I'm messed up her battery when she let me jump start my car. I'll get her a new battery tomorrow and hope for the best. I would try and jump/trickle charge it but I'm fairly sure that as the battery has got that low it will be toast.
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