• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Brake light Problems

Share this page

BabaKahawa

BabaKahawa

Jedi Knight
Offline
I am unable to get my rear brake lights to work. First one side went out then the other.
The driving lights works. I have tested the brake contacts in the socket and they do not light up. How can I test the brake sensor in the engine compartment to see if it works? The supply tank by the wheel well was about half full so I filled the outer portion of the tank. there is also an inter cylinder in the supply tank, it that like a front and rear brake fluid reservoir within the supply tank?
Any suggestions would be appreciated.
 
BabaKahawa said:
I am unable to get my rear brake lights to work. First one side went out then the other.
The driving lights works. I have tested the brake contacts in the socket and they do not light up. How can I test the brake sensor in the engine compartment to see if it works? The supply tank by the wheel well was about half full so I filled the outer portion of the tank. there is also an inter cylinder in the supply tank, it that like a front and rear brake fluid reservoir within the supply tank?
Any suggestions would be appreciated.
Click to expand...
How much pedal pressure do you use? Try pressing down on the pedal with the engine running (car with a booster), and see if it thebrake lights work. I've had a few original hydraulic swithches that required excessive pedal pressure to work. I now use a mechanical switch instead and it activates with a slight foot touch to the brake pedal instead of like the old style that required more pressure. It also comes on instantly which is great in letting cars behind you know that you are applying your brakes and gives them more time to react.
Patrick
 
The reservoir is for the brake (outer) and clutch (inner); it's not a split circuit.

Use a clip lead across the brake light switch (near the rt fr wheelwell) to see if you're getting brake lights. If yes, and it doesn't work without the cliplead and stepping on the pedal = bad switch. If there's still no brake lights (with the cliplead across the terminals) next step is to troubleshoot the turn signal relay (left front wheelwell).
 
My sense is that the hydraulic brake switches fail in stages--at first they are fine, then they require just a bit more pressure and eventually they fail entirely. The fact that one side fails before the other indicates to me a problem separate or in addition to the switch itself.

I always try to bleed air out the line when replacing the switch, making sure that a bit of fluid seeps out as I tighten down the replacement.
 
if you replace the switch filling it with a little fluid first is never a bad thing. This reduces the air you introduce.....


Michael.
 
I did test the brake light switch by using a lead from one screw head to the other.
I also connected the wires together, no brake lights came on.

I guess it's off to the flasher unit/turn signal relay.
Anything special that should be checked first?
Would I see something obvious like a burn contact?

Thanks for all the help so far.
 
Baba--

Simply jumping the contacts only tests electrical continuity--it does not test how much actual pressure it takes to activate the switch and that is, I believe, the failure mode.
 
Do you have -12VDC (or +12VDC if the polarity was swapped) on one (1) of the wires at the brake light switch? That is the first thing to determine.

Michael, if he's not getting brake lights by jumping the terminals on the switch, that wouldn't condemn the switch, as the fault has to be upstream of that. If jumping the terminals did illuminate the brake lights and pushing the pedal did not, then yes, the switch would be at fault.
 
"Michael, if he's not getting brake lights by jumping the terminals on the switch, that wouldn't condemn the switch, as the fault has to be upstream of that. If jumping the terminals did illuminate the brake lights and pushing the pedal did not, then yes, the switch would be at fault"
---------------------------
Agreed. My only point is that I believe the way the switches themselves fail is often gradual so that as they age they require more pressure for the plunger or whatever is inside the switch to active the parts that make the contact, etc.

As an example, my Elva race car does not have any relay box but merely a hot wire energized by the ignition switch that runs directly to the brake switch and on back to the brake light bulb in the boot and on to ground. Prior to each race we go through tech and are told to turn on the ignition and step on the brakes to check that they are lighting up. I did this and passed tech. Following a practice session a competitor told me that my brake lights were not always lighting up where there is a fast sweeper and little brake effort is required to get down to corner speed but that they wre lighting up at a hairpin.

That told me that when I stamped on the pedal at tech and at the hairpin the pressure was sufficient to close the circuit and light the brakes, and that with moderate to light pressure the plunger was not moving sufficiently to make the circuit happen.

Since the switch has rubber parts in it and is susceptible of deterioration I simply think this is one more avenue to consider--usually an easy one to eliminate by simple R & R than by having to test the whole relay board, etc. Since having brake lights that work is required for me me to race I always carry a spare switch--it takes but 5 minutes to replace, and again don't forget to let a little fluid escape so as to bleed out any bubbles which would probably have some effect on actuation, if only until the bubble has been displaced by fluid.
 
:savewave:

Loud and clear you simply do not have power to your brake light circuit.-Fwiw--Keoke
 
check for power at the switch and if there is p0wer and bridging the 2 switch wires still doesn't work then check wiring and connections to the brake lights if there is no power then work backwards and check wiring and connections to the supply source
 
I have been following the wiring, i do not have a wiring diagram, but there is one on the Wiki section of the BCF. Is it ( BJ8 Phase 2 3000 ) similar the that of the BN6. If so, shouldn't the green wire from the fuse to the brake switch always be hot?
Isn't that the power for the brake light circuit?
 
Hi Baba,
The green wire going to the brake switch is switched power (I.E. key on), not always hot. While that portion of the wiring diagram is the same as your car, there are many differences that I would suggest getting the correct diagram. The shop manual and owner's handbook have it. You can also get color diagrams from Tom's Import Toys and I think a guy sells them on Ebay. I haven't tried any of those however.
 
Greg;
Nice site ( Tom's Import Toys )
Thanks for the info.
 
Looks like I found the problem.
Thanks for all the information.
It's time to order parts.
 
Back
Top