• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Brake lights always on

Share this page

drooartz

drooartz

Moderator
Staff member
Gold
Country flag
Offline
I've got one thing to sort out before I can get the new Bugeye through the safety inspection -- the brake lights. Currently they come on as soon as the key is turned all the way to "on" and stay on. Haven't had a chance to dig in yet.

Planning on pulling the wires off the pressure switch to see if I can make the lights go on and off, and probably will test the switch with a test light.

Anything else I should look into right off?
 
Possibly the only other thing I might check as long as you're under the dash is to see if the brake pedal is fully depressing the switch all the way. Maybe check the spring tension or a little lube on the brake pedal. With all that said, I'm guessing it just might be a faulty switch.
 
Sounds like the switch is stuck - or a bad ground.
 
drooartz said:
I've got one thing to sort out before I can get the new Bugeye through the safety inspection -- the brake lights. Currently they come on as soon as the key is turned all the way to "on" and stay on. Haven't had a chance to dig in yet.

Planning on pulling the wires off the pressure switch to see if I can make the lights go on and off, and probably will test the switch with a test light.

Anything else I should look into right off?
Click to expand...


The wiring of the pressure switch is one leg is hot once the key is one (green wire from fuse block), supplying power thought the opposite terminal (green/purple) wire to brake lights. Most likely the switch is stuck in the closed position, but look for a stray strand of wire that might be bridging the terminals. Some people are pretty sloppy about connecting the wires. There can't be much else going on.
 
Thanks for the thoughts. Will check tonight when I get home.
 
I assume you are talking about the hydraulic switch not the pedal actuated switch used on later cars.

If the car has been converted to DOT-5 brake fluid the switch has likely failed. You can install a new one but anecdotal information on the web indicates the new switch won't last long. It is not uncommon when using DOT-5 fluid to leave the failed hydraulic switch in place but remove the wires and run them to a pedal actuated switch instead. Of course, on early cars that requires a bit of fabrication to make a switch bracket.
 
dklawson said:
If the car has been converted to DOT-5 brake fluid the switch has likely failed.
Click to expand...

PO did switch to DOT-5... so failed switch is likely I guess. If that's the case I'll replace the switch for now, and eventually sort it all out when I go through the brake system.
 
Paul Rego in the Triumph part of this board didn't like the generic, plastic, pedal actuated brake light switch used on later cars. They have a reputation for not lasting long. Instead he found a good alternative was the brake light switch for a BMW 2002. They are heavier and of metal construction. Paul has not reported any failures since he started using the BMW part. If you decide to adapt a brake pedal switch you may want to consider the BMW part yourself. When I last looked into this, Rock Auto had the best prices on the BMW switch.
 
When the lights switch is turned just to have the parking lights on, are the brake lights on then or only when turned all the way ?

Could it be as simple as the wires are crossed inside the rear lights ?
 
Just got home and checked, and the pressure switch is bad -- stuck as if pedal is down. Ordered a new switch and a new 4-way union, as I remember the trouble I had getting the one on the Tunebug apart. Actually, I never could separate the switch and union and just had to replace both bits. See, I can learn from my past problems. :grin:

Get this fixed and I should be able to get through the safety inspection so I can be legal.
 
dklawson said:
I assume you are talking about the hydraulic switch not the pedal actuated switch used on later cars.

If the car has been converted to DOT-5 brake fluid the switch has likely failed. You can install a new one but anecdotal information on the web indicates the new switch won't last long. It is not uncommon when using DOT-5 fluid to leave the failed hydraulic switch in place but remove the wires and run them to a pedal actuated switch instead. Of course, on early cars that requires a bit of fabrication to make a switch bracket.
Click to expand...

Yep, heard many a complaint of this switch failing with a DOT-5 conversion.
 
I run DOT-5 in the Mini and the hydraulic switch failed within a month of the conversion. Since I have a lot of take-outs and industrial junk at home I adapted a MicroSwitch to the pedal box. It has served me well for years. If I were faced with this again I would probably use the BMW pedal switch as it has a long threaded body that would make adjustment easier than my current setup.
 
When I eventually convert this car to disc brakes I'll switch back to DOT-3/4, but for now I got a spare switch just in case. Will probably look at that BMW switch conversion as well.
 
dklawson said:
I assume you are talking about the hydraulic switch not the pedal actuated switch used on later cars.

If the car has been converted to DOT-5 brake fluid the switch has likely failed. You can install a new one but anecdotal information on the web indicates the new switch won't last long. It is not uncommon when using DOT-5 fluid to leave the failed hydraulic switch in place but remove the wires and run them to a pedal actuated switch instead. Of course, on early cars that requires a bit of fabrication to make a switch bracket.
Click to expand...

I rebuilt the brakes on my MGA that had been sitting for a long time and the original pressure activated switch was bad. Replaced with a new switch and with the dot 5 I put in the system it failed almost immediately. I put the blame to the parts we are being sold today. I have since converted 2 other cars with original pressure switch's with no problem. On the MGA I made up a mount for a pedal activated switch.
Virtually every car made has a pedal activated switch so if you know where a junker is your cost could be just your time. Frank C had a favorite that was very available and cheap but don't remember what that was.

Kurt.
 
I have seen explanations and conjecture on other forums concerning why hydraulic switches fail with DOT-5. It is not unique to British cars.
 
Turns out it was a failed switch in my case. Happily, I was able to get the switch and 4-way union separated without breaking anything (I had a spare union just in case).

When I get around to doing the disc brake swap I'll probably switch back to DOT 3/4.
 
dklawson said:
I have seen explanations and conjecture on other forums concerning why hydraulic switches fail with DOT-5. It is not unique to British cars.
Click to expand...

Yes, I've read that some of the rubber is silicone based and does not work with dot 5. Also other problems. My MGB is now owned by a friend and has now done 100K with it with no issue's so I am still sold on it. The B was only a few years old when it needed a complete brake rebuild and I used the then new dot 5 in it.

Kurt.
 
Go figure. The life of those switches seems to defy explanation.

I have been told that there is a hydraulic brake switch for Harley's that will work in place of the original switch but I don't know if people are fitting it because it holds up better to DOT-5... or if they are using it simply because they can buy it locally.
 
Instead he found a good alternative was the brake light switch for a BMW 2002. They are heavier and of metal construction.
Doug, Questions on the BMW switch: I assume the thread on the switch is different than the original POS lucas switch. Do you modify the threads on the switch itself, or re tap the pedal bracket? Is there a particular year that is preferred for the replacement BMW switch. If you would elaborate on the swap, or direct me to the original source that details what is necessary for the change, I would appreciate it.
 
I have not done the switch swap on a car that came from the factory with a pedal box mounted brake light switch. All my early LBCs came with hydraulic switches so the conversions I have done involved making a bracket to mount the switch. From memory the Lucas-type plastic switches I bought were threaded 1/2-20 and came without mounting nuts so I never used them. I was not interested in making a pair of 1/2-20 jam nuts to mount a switch I bought for less than $3 (yes you can pay more but BP Northwest sells them for less). I currently have a surplus industrial MicroSwitch on the Mini instead. Our Spitfire and GT6 both still use the factory switches.

Were I buying pedal switches now I would go to RockAuto and look for the brake pedal switch for an early 1970s 2002. You should be presented with two choices one which will be from Airtex. If the pictures are to be believed, the Airtex switch comes with two jam nuts while the other product does not show nuts. I assume the BMW switch must be metric. Regardless, to fit it to an early car will still require making an "L" bracket to attach to the pedal box and that bracket should only require a through-hole so the thread type would not be important.

If you were trying to adapt the BMW switch to a car that uses a tapped mounting hole for a factory pedal box mounted switch the thread type would matter of course. However, you could drill out the existing "nut" on the mounting bracket and use two jam nuts on the switch. I cannot even speculate regarding what would be appropriate for your car.


EDIT: I was wrong in my earlier post. It was not Paul Rego who found the BMW switch, it was "BobbyD", also from the Triumph part of this board. You can see his write-up of the switch in the link below.
https://tr6.danielsonfamily.org/AltBrakeSwitch.htm
 
Last edited:
Back
Top