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Brake light indicator mod

Discussion in 'Roadster' started by slcasner, Mar 7, 2013.

  1. slcasner

    slcasner Member

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    Ever since getting the Roadster, I've wanted a light on the dash to indicate when the brake lights come on as a result of the deceleration due to regen braking. Several of the vehicles converted to EVs by AC Propulsion have included this feature. I never got around to implementing this idea because of the lack of a vehicle shop manual to help with finding the brake light wire and figuring out how to run the wiring to the dash.

    Recently I came up with a better idea: mount an LED indicator light in the housing of the center brake light inside the rear window so that the LED shines directly at the rear-view mirror and into the driver's line of sight. This is a very simple installation because the brake light circuit is right there already, and it is a better location for observation than my original dash idea since the times when I care about the brake light being on typically the same times when I'm checking the mirror to see if someone is close behind me.

    A poor-man's version of this might be achieved by simply drilling a hole to let light from the brake light shine forward, but I don't think that would be bright enough. Maybe a light pipe would work. My choice was to install a separate narrow-beam LED so I could have good control over the direction and light level. In case others might want to replicate this idea, I'll provide some construction details. I have a 2008 Roadster 1.5, but I suspect this portion of the design did not change in later models.

    I started by trying to remove the interior dome light from the brake light housing as in this post from S-2000 Roadster about replacing the bulb with an LED. However, that was a mistake because it is unnecessary and not useful for this project. Instead the whole center brake light housing needs to be removed. Before doing so I strapped a little box to the brake light housing so I could hold a yardstick from there to the mirror to guage the angle of the sight line. I determined that the angle is approximately 8 degrees downward from the brake light housing to the mirror, and also approximately 8 degrees toward the passenger side of the car.
    angle-small.jpg

    It is pretty easy to remove the center brake light housing. There are four bolts with 10mm hex heads that hold the soft-covered interior roll-bar panel and the plastic brake light housing in place. Remove the four bolts, being very careful not to drop any parts or tools down behind the seats or they may be gone forever! The push in on the vertical plastic cover on the inside of the B pillar to let the loosened panel drop past. Be careful not to pry the front corner of the interior roll-bar panel because it is just made of molded foam that can easily be torn. In fact, I discovered that the panel in my car had been damaged by someone during original assembly or some previous repair work. I repaired it to some degree with hot glue as shown in this picture.
    repair.jpg

    Two cables attach to the brake light housing, one for the brake lights and one for the dome light. Both will release pretty easily if you push in on little tabs. Once the brake light housing is disconnected, you can remove the strip of LEDs that form the brake light by pushing back the clips to release the circuit board.

    The first step is to drill a hole in the housing for the LED. I chose a red LED with a 5mm diameter clear resin body and narrow viewing angle from my parts bin. The hole needs to be fairly close to the lower surface of the housing in order to not be coverd by the interior panel, and should be near the center portion of the housing that extends further to hold the dome light. The following picture shows the position. When drilling in plastic, it is best to drill the finished-size hole on the first pass rather than drilling a smaller pilot hole first because the larger bit is likely to grab in the pilot hole and tear the plastic. Remember to account for the downward and rightward 8 degree angles when drilling.
    position.jpg

    The next step is to mount the LED. I used hot glue for this. To hold the LED at the correct angle and position I used a little block of wood and a C-clamp, then glued the LED in place. I wanted to minimize the amount that the LED protruded from the front of the brake light housing.
    block.jpg glue.jpg

    Then I soldered a pair of wires onto the brake light circuit board where the cable attaches. These wires must be bent back sharply because the end of the circuit board fits tight against a plastic support in the housing.
    solder.jpg bend-back.jpg

    A resistor is needed to limit the current and drop the 13.5 V supplied by the car down to 2 V across the LED. I was concerned that the LED might be too bright and therefore be distracting, especially at night, so I started out with a 1 K ohm resistor, which results in about 10 ma current. What I had not considered is that at night the mirror will be flipped to night mode to avoid the glare of headlights behind, so that makes the relative visibility of the LED about the same in daytime and nighttime. Furthermore, the LED was not bright enough to be easily disinguished from the red signal lights visible in the mirror. I reduced the resistor to 500 ohm, allowing about 20 ma current, and that works better. Keep in mind, though, that the LED I selected from my parts bin has probably been sitting there for 20 years, so it is not as bright as modern LEDs for the same current level. If you get one of the high-efficiency LEDs that puts out 10,000 mcd at 20 ma, it would be way too bright. This shot shows the resistor soldered in place; the glue job looks ugly because I had not considered the 8-degree rightward angle, so I needed to soften up the glue and try to re-orient the LED.
    resistor.jpg

    Fortunately, it is easy to select the right current level by trial and error. Just tack-solder in a resistor that you think will work, then mount the brake light housing back in the car without the interior roll-bar panel and give it a trial run in both daytime and nighttime. Once you find a resistor value that you like, then you can solder it in more securely and reassemble everthing. My finished result looks like the pictures below.
    finished.jpg
    shining.jpg mirror.jpg
     
  2. Pantera Dude

    Pantera Dude Member

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  3. Doug_G

    Doug_G Lead Moderator

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    Very clever! And simple!
     
  4. vfx

    vfx Well-Known Member

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    Pretty cool!

    In the mirror I can see my brake lights reflecting off the rear wing in all but the brightest daylight.
     
  5. Raffy.Roma

    Raffy.Roma Active Member

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    I think that a brake light indicator should be implemented on all Tesla cars....or at least future Tesla cars.
     
  6. slcasner

    slcasner Member

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    I agree that the reflection from the spoiler is visible at night, but I've never been able to notice it in the daytime.
     
  7. augkuo

    augkuo Member

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    Especially with a red car!

     
  8. Doug_G

    Doug_G Lead Moderator

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    Yes, I can easily see it at night with my red Roadster. White would be almost as good, though.
     
  9. tdelta1000

    tdelta1000 Active Member

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    Two thumbs up for a great mod.
     
  10. Timothy

    Timothy Driving on Sunshine

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    But VFX lives in LA. With that poluted air it is like night in the daytime--not brilliant sunshine like the Central and Northern Californians get! :wink:

    Great idea; great solution!
     
  11. Botbldr45

    Botbldr45 Member

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    Just finished my install of LED as outlined above. Really great .... Got a red LED from superbright.com and followed directions from slcasner. I didn't put a resister in the circuit and the light is very bright making me think a cop is behind me!! ..... Been there done that!
    The light is really a great idea. It lets you know what regen lighting is like and what cars behind you see. It should be on all EVs to let driver know what their brake lights are doing.

    I will probably put a resister in the circuit eventually to reduce the intensity of the LED. The directions are spot on and easy to do ... And I am not an electrical type.... More biological background but this is a procedure I would recommend for all roadster owners.
     
  12. slcasner

    slcasner Member

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    Update: The hot-melt glue did not hold well enough in my implementation of this mod, so the LED pulled back out of the hole. Maybe there was too much solar heating under the black carbon fiber roll bar cover, or maybe I just didn't get the glue around the LED securely because I had to re-melt it to adjust the angle. Anyway, I took out the glue and modified a terminal strip to fit, then soldered the LED, resistor and wires to the terminal strip as shown.
    terminal-strip.jpg
     
  13. mgemmell

    mgemmell Scottish chap

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    In the EU the Roadster brake light goes on only when we hit the brakes. The deceleration force sensor was not allowed here :(
    I was convinced I was going to get rear-ended as a result of virtually never touching the brakes but 2 years on I'm not so sure... but you do need to watch the rear view mirror to check no one is caught by surprise by a slowing car with no brake lights.

    BTW... wouldn't a small piece of silver tape on the outside of the rear window near the edge of the brake light obtain a similar result? A bit scrappy, but....
     
  14. Botbldr45

    Botbldr45 Member

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    Actually I used Gorilla Glue from Lowes Hardware to hold the LED. Seems to be working pretty good........ so far!
    What size resistor did you use??
    The terminal strip is a great idea. Well done!
     
  15. slcasner

    slcasner Member

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    Along with changing to the terminal strip, I reduced the resistor from 500 ohms to 330 ohms to increase the brightness a bit.

    Unless the LED you are using is designed for direct operation on 12V (that is, with a built-in resistor or active components to limit current), I would expect the LED to burn out when connected without a resistor to limit the current. Maybe the brake light LEDs in parallel provide some protection. Still, I would advise against the installation without a resistor because of the risk of overheating.
     
  16. PeterK

    PeterK Model S Owner

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    That seems like a really dangerous EU decision to me. Even in the US I worry that someone will rear-end my S in stop-and-go traffic. I've noticed people getting closer than usual (perhaps they're interested in the car ). I would like to have a brake light indicator, either in the mirror or back window.
     
  17. mgemmell

    mgemmell Scottish chap

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    Totally agree. I was very angry when I got the car, and would touch the brake with my left foot during regen to get the light to come on at first. I even chased the Tesla engineers to reprogram the option (it is, of course, all down to a variable setting).

    But that was a long time ago. Now I just drive it with essentially no brake light (except for the final 1m when coming to a stop).

    Surprisingly, even though people get real close (taking photos, reading the tesla badge...), and even though I make judicious use of regen braking, I have never (yet!) had a scare.

    I have been rear-ended in the past in another car though so I always check the rear-view as I reduce speed. Maybe that is why nothing has happened. In Spain its a good idea to assume everyone is out to run you off the road, fundamentally because they are! ;)
     
  18. Botbldr45

    Botbldr45 Member

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    The LED I got from Superbrite WAS designed and advertised for a 12volt system but it is still very bright. I'm getting used to it now and probably won't change it or decrease the intensity of the light. I can't believe I drove for a year without it....... Very handy!! .....,especially for the *******s in their big trucks that like to putt up on your bumper to assert their dominance I guess .... At least until the light turns green!,.... :)
     
  19. Timothy

    Timothy Driving on Sunshine

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    I decided to try this project--but definitely needed adult supervision. So SLCasner decided to come though Santa Barbara and I asked him to 'supervise' my installation while he was here. I then carefully reread Tom Sawyer. He did a beautiful installation while I took photos which I will try to upload. Thanks for your 'help!'

    - - - Updated - - -

    Regen light on Tesla (5).jpg Regen light on Tesla (1).jpg Regen light on Tesla (3).jpg Regen light on Tesla (4).jpg Regen light on Tesla (7).jpg Regen light on Tesla (8).jpg Regen light on Tesla (9).jpg
     
  20. Botbldr45

    Botbldr45 Member

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