I made this to match the tail lights I am building.
This also includes a bleed resistor on the power supply board so that the ACD will not malfunction due to being switched from incandescent bulbs to LEDs (which is a problem on the CT9A)
This took me about 8 hours start to finish, including design and CAD time.



PCB designed in CAD, and transferred onto copper clad for acid etching.

Components mounted, and ready to be installed. Boards attach with small screws that are hidden after final assembly.

I also "tinned" the PCB to protect the copper, and I used a silicone based conformal coating to prevent moisture exposure.

I had to do some small modifications to the plastic housing so I could access the fasteners.

current draw at the regulated 12V supply is about 550 ma, which is about a third of the factory incandescent bulb.

 

Wow! Super nice & props on the creativity

I love LED's & look fwd to those tails

 

Can you touch upon the problems with going from incandescent bulbs to leds in the rear 3rd brake light? I currently have a led bulb in the 3rd brake light but haven't experienced any issues. Is there a acd light or anything that comes on or does it just feel different? Great mod tho looks really clean!

Here's my 3rd brake light setup https://www.evolutionm.net/forums/pr...l#post11850459 (it's just a led bulb swapped out from the normal incandescent bulb and an inline flasher relay, not a whole panel of leds like you did)

Update: I saw a post you made about it a long time ago saying it only happens with the headlights on. I'm almost positive that I have driven with them on and still no 3 acd lights lit. I'll drive my car around with the headlights on to double check. I just looked at the description of the leds I purchased they have some tech built in called "Constant Current IC Technology, This allows bulbs to be more reliable when used on vehicles that have voltage fluctuations due to electrical system design or fault" quoted directly from the product description. So maybe the bulb picks up the slack or something when the 3rd brake is off and pulling the constant 1.0v then switching to the 12v when the pedal is pressed?!?!?

 

The ACD system needs to know when the brakes are being pressed. It uses a "bias voltage" on the brake circuit and monitors the status. LEDs will not allow current flow if the voltage applied to them is low enough since they are semi conductors. They need enough voltage to meet the thresh-hold value where there can be some current flow (hence the name "semi-conductor")

Your tail light brake lights, and CHMSL are all in parallel. If you have all 3 bulbs replaced as LED, the "bias voltage" coming from the computer is not strong enough to "push" through this setup. As a result, the 3 lights on the ACD cluster will light up solid because it isn't seeing input from the brake pedal. I assume this is not a problem on NON ACD cars.

Test my theory by measuring the voltage at the CHMSL lamp with the key on, but the car not running. (or you can do it with the car running, it will not matter). With my meter, the voltage shows about 1.0V across the connector. In reality I believe the voltage is higher, but the problem is there is so much resistance on this circuit (inside of the computer) that the incredibly high resistance in in the order of the resistance inside of my meter- hence your measurement drastically affects the voltage.

The way around this, is to use a bleed resistor on the circuit. I found that 220 ohms worked perfect, but 1,000 ohms was not enough. (I was just playing with resistors)

You will not see this problem unless all of your brake lights are LED because even 1 incandescent bulb has an very low resistance which will immediately pull this bias voltage to ground. (think of parallel resistance circuit math)

 

Ok so because my rear tail lights are still incandescent bulbs I won't experience the 3 acd lights being lit? Yeah I don't plan on changing my the bulbs in my tail lights so I should be good then right? Or do you still recommend me installing a resistor?

The reason I use a led bulb instead of the incandescent bulb in the CHMSL is because when the flasher relay blinks with the incandescent bulb it would miss the x3 fast flashes as the incandescent bulb has a delay when illuminating. The led bulb has an instant on/off illumination where you can see the x3 fast blinks.

 

You won't need a resistor- you are fine.

Take a second to look at the math. If any 1 R value is low, the effective resistance will be very close to this value.

 

Just an update, I didn't get a chance to check the volts to the 3rd brake light at off position but I did drive to work with the lights on this morning and you're correct no 3 acd lights on. Weird tho that others would comment about the same issue and not mention that they had swapped the tail light bulbs to led as well (they only mentioned that they swapped the 3rd brake light back to incandescent then it worked correctly again). Good to know that you can swap out the 3rd brake light with led but not the actual tail light bulbs and not have a problem.

Thanks for the fix! can't wait to see your led tails !!!!!!!!!!!!

 

https://www.evolutionm.net/forums/ev...t-evo-9-a.html