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Jul 19

Manual Headlight Level Adjuster for the RX8

Note, before you start cutting wires in your car: the internals of the headlight auto levelling system are unknown to me I’m treating it as a “black box” (how convenient that it is actually a black box) and just looking at the inputs and outputs and making assumptions about how it works. I accept no responsibility if you cause damage to your car, yourself or others from doing things detailed in this post.

Background on HID lights

All 231BHP versions of the RX8 (in the UK at least) have high intensity discharge headlights (HIDs).

One of the requirements for using HIDs in a car is that the car must have some sort of auto-levelling system to ensure that when the car is loaded unevenly front to rear that the difference in height front to back does not cause the lights to point too far up, potentially dazzling other motorists.

The RX8 does this by having actuators in the headlight unit to angle the beam up and down. To sense the suspension load at the front and rear it has 2 sensors, one on the left front suspension, another on the rear left suspension assembly.

So what’s the problem?

So you may be thinking why do you want to manually adjust the lights then? Surely this is a safety feature?

The sensors are, essentially, potentiometers (variable resistors) attached via a linkage to the suspension. They have a wiper that moves along a carbon track the ends of which are connected to power and ground.

It costs £400to make this? Really?

By reading the voltage from the wiper connection on the front and rear sensors the auto-levelling control unit can work out if one end of the car is higher than the other and adjust the headlight angle accordingly.

The problem is that the sensors that are used, corrode and wear out. This wouldn’t be so much of a problem but Mazda want around £400 per sensor! For a variable resistor?!

So there we have it:

  1. Give £800 to Mazda for some new sensors
  2. Attempt to repair the sensors (if you’re lucky you may be able to dismantle the sensors, give them a good clean, replace contact springs and they might start working again)
  3. Go manual

How to do it

Fortunately Mazda have made this quite simple to do as the headlight auto levelling control unit is in the cabin and not, for example say, part of the ECU, or in some inaccessible location.

The control unit lives just to the left of the glove box, to get best access to it, remove the glove box, this involves gently bending in the side of the glove box when it’s open to allow the end stops out, once that’s done you should just be able to lift the glove box out (there is also a soft opening mechanism, but mine died quite some time ago, as far as I know you can just unclip it from the glove box.

[AUTO LEVELLING CONTROL UNIT PICTURE Coming Soon!!!]

The auto levelling control unit is the black box that says “Auto Leveling Unit” on it. It has one connector with 24 pins, the details of which you can see below:

This is as seen from the cable side of the connector

From the RX8 wiring diagrams the cables we care about are :

  • P – Black with a Green Stripe – Ground for sensors
  • C – Black with an Orange Stripe – Power for sensors
  • I – White with an Orange Stripe – Rear Sensor wiper output
  • K – Black with a Blue Stripe – Front Sensor wiper output

So what we want to do is tell the auto levelling unit that the front suspension is at its neutral position all the time and we want to be able to adjust the “rear position” to make the unit think the boot is either lightly or heavily loaded to make it adjust the headlight level accordingly.

So here’s a simple little circuit to do just that, you will need:

  • 2 x 4.7k Resistors
  • 2 x 1k Resistors
  • 1 x 10k Linear Potentiometer

What you need to build

R3 and R4 are there to change the range output by the potentiometer, as the auto levelling control unit most likely flags a fault if the voltage is zero or maximum (implying a short or open circuit somewhere).

So simply build it up in whatever fashion you desire (do make sure to insulate the parts from each other) and put it on a long enough wire to locate the potentiometer somewhere you can get at it, I think the ashtray would make a fine home.

Before starting the install, disconnect the negative battery lead. Installing it is a matter of cutting back a bit of the massive amount of insulation tape on the cable to the auto levelling unit connector then cutting the 4 wires detailed above (check twice, cut once). Strip a short length on each of the 4 cables from the connector (insulate the other ends, they are not used, they’re just connected to your broken sensors) and then either solder, or use terminal blocks to connect your contraption.

11 comments

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  1. Sean

    Hey Alex, thanks so much for the work on this diagram and info, I’m ready to try this out! But, got one q though about the wattage of the resisters involved in this circuit? What do you think I should buy for them. I heard that 2 watts is pretty good…..let me know if you get a chance. Thanks a ton, Sean, white lake, mi

  2. alm

    Hi Sean,

    1/4 or even 1/8 Watt resistors should be fine for this as the current is pretty low. If we look at the chain with the lowest resistance (and therefore highest current), R1 + R2.

    I = V / R
    I = 12V / 9400ohm
    I = 0.0013A

    P = I * V
    P = 0.0013A * 12V
    P = 0.015W

    Hope this helps

    Alex

  3. carl

    Hi Alex.

    I am a sole Trader Garage.

    I built and fitted your H/Lamp adjuster circuit and fitted it to a customers Vehicle, as he could not afford to replace the Actuators which upon opening up, were totaly shot.

    Upon operating the lights the Vehicle burst into Flames and Burnt Down My Garage.
    Thanks.

    Only Joking; the unit worked superbly and the owner was well pleased & I made some Money which is a result in these hard times.

    I you would like to let me know what your Favourite Charity is I will Donate a small amount as a token of my appreciation.

    Carl

  4. alm

    Good job Carl. One thing you might want to point out to your customer is that the headlights can only be adjusted when the vehicle is stationary, makes sense really.

    If you’d like to make a donation to a charity then Diabetes UK would be my charity of choice.

    Glad I could be of some help to you.

    Alex

  5. Carl

    Hello again Alex,

    Will do as regards Charity.

    Yes thanks was aware.

    Also if anyone else makes up this Circuit its worth pointing out that there is a slight time delay of a few seconds when moving the potentiometer and the H/Lamp movement and that the adjustment is quite sensitive so turn a very small amount until you get the “feel”. I point this out just in case there is a risk, that the adjuster Mechanism may get to the end of its working limit and break something in the w Headlamps as is the case with some vehicles ie, the adjustment Gears strip or Internal reflector comes adrift.
    Thanks Again, Carl

  6. Carl

    Hello again Alex,

    Will do as regards Charity.

    Yes thanks was aware.

    Also if anyone else makes up this Circuit its worth pointing out that there is a slight time delay of a few seconds when moving the potentiometer and the H/Lamp movement and that the adjustment is quite sensitive so turn a very small amount until you get the “feel”.
    I point this out, just in case there is a risk, that the adjuster Mechanism may get to the end of its working limit and break something in the Headlamps as is the case with some vehicles ie, the adjustment Gears strip or Internal reflector comes adrift.
    Thanks Again, Carl

  7. Jerry

    This is just brilliant. Thank you so much.

    I’ve been arguing with Mazda, writing letters to the CEO etc. about having to pay a fortune back to Mazda to fix a problem which is clearly a design fault.
    All to no avail, so I’ve been driving round dazzling people and with an intermittent (why is it only intermittent!) warning light on the dash board.

    This solution cost me about £10 in components and only took about an hour today (mostly reminding myself how to solder components onto a PCB!). Brilliantly clear instructions and IT WORKS!

    One little suggestion. I was trying to figure out where best to fit the potentiometer – even your suggestion of the ash tray sounded like a fair bit of fiddling around. So I went for a lazier approach. If you open the glove box there is a switch on the left hand side to disable the boot opener. I discovered that there is enough space just above this to mount the pot and still allow the glove box to close. Given that it’s not something I will be adjusting much (once I have set it correctly) this seemed like a pretty handy place to tuck it away, with less chance of it getting accidentally knocked.

    Thanks ever so much

    Jerry

  8. rere

    Alex…You’re the man of the day. Thanks to you, I’m happy again. You did a great job posting this solution. Under 15$ and 2 hours work, instead at least 500$. Maby someday someone from Mazda will call you for a great job offer. Or you will get some benefits from them if you’ll keep your ideas for yourself.

    rere Mt Prospect, Illinois

  9. Eddie

    Hi Alex,
    what an elegantly simple and ingenious solution! Brilliant! I’m making a run to my local radio-shack to pick up the components and give it a try.
    I’m curious, how did you figure out the required resistance for the various resistors used?
    Thanks so much for posting this solution and such detailed instructions to go along with it.
    Diabetes UK will be getting another modest donation!
    Eddie Princeton, NJ

  10. Marc

    I’m just about to try this, has anyone tried finding the end of the wiring loom behind the blank switch next to the DSC? It appears to fit a mazda headlight level switch.

    Has anyone tried a ‘plug & play’ version using parts from a 192 RX8?

    Thanks

  11. Matt Earle

    Hi Alex

    Thanks for writing this solution up.

    I fitted it last week and it worked perfectly!

    Thanks

    Matt

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