Brake lights on permanently - MOT Fail - Help!

Post by **GeorgeHurst** » Thu Jul 16, 2009 3:39 pm

Hi there,

Just failed my MOT as my brake lights stay on all the time, I know there could be a million explanations for this, but I was hoping someone might give me a hint as to where to start.

I'm going to check that everything is earthed correctly, and then check all connections, but after that I'm not sure...

Also, I had some advisories including: ' N/S and O/S front radius arm has slight play in a pin bearing' - I have very basic knowledge of suspension, any help for how to go about remedying this?

Many thanks in advance,
George

Post by **bmcecosse** » Thu Jul 16, 2009 3:48 pm

Brake lights are actuated by a pressure switch - so it may have failed - or there may be excessive pressure in the system. Even first thing in the morning - before pressing the brake pedal - are the lights on then ?
Front radius arm pin bearing - hmm - could be a number of things, always best to get the garage to point out excatly what they feel is wrong - and usually they will tell you how to fix it! I would say it's probably the inner pivot for the lower suspension arms - which run on rubber bushes - on a 'pin' - inside the eyebolt which sticks through the chassis. Not too serious and not too difficult to fix. Do you have to get it back to them inside the 10 day period to get a 'free' retest? If so - better order up the bushes asap - your choice whether to get rubber or polyurethane - and strip the suspension while you wait for them to arrive. Ask for 1st class post - I got parts for my TR7 yesterday by phoning up Rimmers - placing the order with credit card - and Postie had them at my door by 8am next morning.
If you don't have the workshop manual - PM me and i will send the link.

Post by **GeorgeHurst** » Thu Jul 16, 2009 4:03 pm

Thanks for the advice BM, pm on its way, i was actually browsing ebay for a workshop manual this morning so that would be awesome, thanks.

Brake lights are on as soon as the car starts up, is there a way of testing if the switch has failed (so I don't buy an unnecessary part)? I do get a 10 free retest, so will get the bushes ordered today (going to go with poly).

Cheers, G

Post by **bmcecosse** » Thu Jul 16, 2009 4:23 pm

Pull the wires off the switch - lights should go out. However - it could still be pressure in the system - OR a failed switch. Do you have a servo ? You say - whenever the 'car starts up' - so are they ok until the engine is started ?

Post by **d_harris** » Thu Jul 16, 2009 5:14 pm

Pull the wires off the switch (on the drivers side in the front corner of the bonnet floor) are the lights still on? Theres a short somewhere (check in and around the light bases at the back of the car)

Not on? Get a multimeter or test lamp and check to see if there is voltage across the two pins - if there is, you have your answer - faulty switch. Easy replacement, but remember to bleed the brakes after

Post by **polo2k** » Thu Jul 16, 2009 6:50 pm

I dont think anyone has mentioned where the brake light switch is, its bolted to the engine bay floor and has 3 pipes and 2 wires going to it. the 2 wires go into what looks like the head of a 23mm bolt. it is under the dynamo/alternator (under the drivers side end of the radiator)
To check the wireing use a mulimeter and set it to the 20Vsetting (or whatever is reccomended for 12V max) and you should have 12V on one of the wires and 0V when you test the other. to do this touch the black probe to some clean metal on the body and the red to one wire and then the other on the switch connector.
To test the switch set your meter to continuity (sometimes an arrow or called diode test), look at the screen and it will say a number, touch the 2 probes together and it will change. if you touch the probes to the terminals on the brake switch they should stay as the first number until you press the brake and it will go to the other.
If the number on the screen is the second when your not pressing the pedal then your switch is shot.

Sorry Dan, I think it was just a wording error

Post by **bmcecosse** » Thu Jul 16, 2009 10:42 pm

Yes - but the switch could be closed because it is faulty - OR because there is some residual pressure in the system! Hence my suggestion of check first thing in the morning. if the pressure appears when the engine is started - could be a faulty servo - if the car has one fitted. Waiting to hear about that!

Post by **Pascal** » Fri Jul 17, 2009 3:40 pm

Got the same problem some time ago, which came down to a faulty switch. Given the trouble in replacing it and reports of unreliability of such switches, I got a microswitch from Maplin and fitted it on the floor by the brake pedal. Wires just derived to original switch. Very simple and reliable.

See details on the original thread:

http://www.mmoc.org.uk/index.php?name=P ... highlight=

Post by **GeorgeHurst** » Fri Jul 17, 2009 3:53 pm

Right... sorry for the delayed reply, and thanks for the advice.

I've let the car sit over night and haven't pressed the pedal once yet so presumably not an issue with residual pressure. The brake lights come on as soon as the igntion is on and also when the engine is started.

BM - I don't have a servo fitted.

I've taken the wires off the switch and the lights go out, so its looks like it is the switch that's at fault. I don't have a multimeter unfortunately, so for the £5 that a new switch costs I am just going to replace it, and hope thats it sorted.

Pascal - the microswitch sounds like a good plan, thanks, but for the sake of ease I'm just going to replace the original switch.

Cheers, George

Post by **bmcecosse** » Fri Jul 17, 2009 5:00 pm

Yes - it must be faulty switch then - problem is -some of the replacement switches these days are renowned for not lasting very long ! If you can find a new-old -stock switch that is likely to be very much longer lasting!

Post by **8009STEVE** » Fri Jul 17, 2009 5:27 pm

IIRC a previous thread said to get a land rover switch as they were better.

Post by **GeorgeHurst** » Fri Jul 17, 2009 6:38 pm

Yeah... the other thread reccomends the following... I'm going to try and look one of these out if poss...

"the brake light switch to buy is made by Quinton Hazel, the same as those fitted to Series Land Rovers"

Post by **bmcecosse** » Fri Jul 17, 2009 6:48 pm

I'm sure Matt Harris had some of these a while back. You could PM him!

Post by **Matt** » Fri Jul 17, 2009 7:23 pm

I used too.... but no longer (at least I dont know where they have gone

)

Post by **polo2k** » Sun Jul 19, 2009 12:24 pm

does anyone know what pressure these operate at? the reason I ask is at work we can get some presswure switches but they would use different connectors. is the thread 1/4bsp? (or taper?) what is the max pressure when the pedal is stomped on?

Post by **bmcecosse** » Sun Jul 19, 2009 8:41 pm

Pressure could go as high as 1000 psi in an emergency - but normally a few hundred psi. Would expect switch to close at ~ 20 psi ?

Post by **polo2k** » Sun Jul 19, 2009 9:29 pm

Ill try and remember to have a look in that case.
There would probably be a minimum order so ill see what that is. If there is enough interest shown here then ill start a new thread (presuming its all feasable)
Ive anyone has ben watching this and thinking "hmm I wouldnt mind a better switch" then make your self known

p.s. does anyone know the thread on the switch?

Post by **GeorgeHurst** » Mon Jul 20, 2009 7:36 pm

FYI All fixed and MOT passed today

thanks for the advice chaps

Post by **polo2k** » Mon Jul 20, 2009 11:06 pm

was it the switch?

Post by **bmcecosse** » Mon Jul 20, 2009 11:10 pm

Well done GH!