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Discussion Starter · #1 ·
The Pictures Can Be Found Here:

This document has been transcribed to be posted here for the benefit of all members. It is intended to be viewed without charge. If for any reason this site intends to charge people to view it, it must be immediately removed from this or other website unless through the consent of the author: pIOUs
Warning: The following document is meant to chronicle a project I attempted. This procedure was carried out with care and is by no means meant to imply that everyone can accomplish this project. I realize the risk of permanently damaging my vehicle and take it because the faith in my technical abilities. Anytime you alter the original circuitry, you must take precautions to limit the chance of fire and electrical shock. I must assume that you have taken the necessary precautions like eye safety etc. in addition to this before proceeding with this kind of project.

The following is a write-up on one way to retrofit the backlighting of your 5th Gen Honda Prelude (Most apply to a 4th Gen as well) with blue super bright LED lamps. This should remedy the desire to change the color of your dash lights to any color you wish so that it will match your other electronics.

Most people want to know what's involved before they decide if they want to undertake the project. Upon review of the write-up, some of you will prefer to hire someone who has done this already to do his or her retrofit. With a write-up will come more apt specialists who are in you city/town. That means you may have to wait to get this done and the alternative means shipping your unit off for some unknown period of time IF you can figure out how to remove the climate control.
Who can stand not having A/C in their car? Not me! Some local friends/club mates want me to do their retrofit for them, but coordinating this has been a PITA. I need to keep the thing for a few days and I have to go to them and remove their unit even though most of them could do it if they had some clear directions.

I have decided to include some basic directions for uninstalling the climate control and bypassing the mode control switches and driving circuit.

Unfortunately it's not as simple as leaving the fan speed switch attached to the car because the AC compressor will not come ON. I have found a way to short the necessary pins so that when you click on the fan, the A/C works. This should lesson the burden of having your Climate control away for a while, even though you won't be able to change much after you remove it.

So, the procedures marked with an asterisk will apply only to those who will have their Climate Control removed for several days while the retrofit is taking place. The parts listed below give rough quantities for purchasing LEDs. You need to weigh in the fact that some may be broken burnt out or yield a strange luminous pattern (Our you may do this during the project). Note the pictures provided so that you can plan what LEDs will go where. There are 8 buttons that need backlighting. 1 of those should be done in red (defrost). That means there are 8 indicators (where the recirculate one is orange). Then you will require 2 Blue 3mm, 1 blue 5mm, and 1 red 5mm For the lower part where the temp slider is.

· Premium Member
1,412 Posts
Discussion Starter · #2 · (Edited)
Here is the breakdown:


Supplies, and Tools
  • A 20-40 Watt soldering Iron. For most of the work you will only need the 20Watt iron, but when you mount the LED Cathode to the frame, it will cool down too much because of the large surface area.
  • Dremel with carious bits (pic 06)
  • Hot glue gun.
  • Calculator for resistor calculations.
  • Wire stripper.
  • Solder and flux.
  • Multi-meter with DC voltage, continuity, and resistance functions.
  • 20 gauge single core/solid copper wire.
  • Various needle-nose pliers, Phillips screwdrivers (including 1â€? and 8â€?), exacto-knife, additional pair of hands, Black Sharpy pen, etc (pic05).
  • 12v power supply or dry-cell equivalent for testing.

Removing the Climate Control Assembly

  • *) Turn on your car and make sure the A/C is how you usually have it set. The mode control and re-circulate will remain as they are once the car is turned off and the assembly removed.
  • 1) Pry forward the slider knobs with a protective flathead screwdriver. Be sure not to scratch the plastic under the knob and that you are pull straight out (pic07).
  • 2) Remove the center console bezel (2 clips per side, 1 bottom, 2 top clips). I usually find it best to pull from wheel the accessory plug is at the bottom and then pull the top out with the gap that is made (pic08).
  • 3) Remove the 4 screws that mount the radio/pocket bracket and pull the assembly forward. It is possible to get the Climate Control out while leaving it plugged in, but it will be easier to manipulate everything with it completely removed. Just make sure you have the Radio code if yours is factory and that the shifter is pulled away from it (pic09).
  • 4) Remove the Climate Control (CC) plugs. The green one pulls down when you release the clip facing the rear, and the brown one pulls out straight back when you release the clip (pic12).
  • 5) Remove the 4 brass colored screw from the CC. Pull it forward at turn it counter clockwise so that you can take of the temperature cable (pic10).
  • 6) To release the cable, unscrew the small brass screw holding in the silver retainer plate. Unscrew the large brass screw for the cable stay bracket. Pull down the black plastic arm enough to get the cable off the pin. Make sure the springs and stuff stay in place when prying it down (pic11).
  • 7) Once you have the CC out. Reassemble the brackets for safe keeping (pic14). You can also remove the 3 stock bulbs from their seats by a quarter turn counter-clockwise.
  • 8) Remove the fan speed switch by unscrewing the 2 small brass screws on either side. Also, get the one small brass screw from the other end of the CC (pic13).
  • 9) *Now plug the switch back into the brown plug and short pins 1 and 2 on the green plug. Shorting the BLUE/RED and GRN wires will make allow the fan-speed switch control the A/C compressor as it would with the CC connected (pics04&15).
  • 10) Remove the CC faceplate by prying back the 3 clips on the top and bottom (pic16). I find it easiest to start with one side and work my way to the other. Remember that each of the face buttons are attached to the switches inside with individual clips so don’t worry about the resistance they give you when get the face off. Just get the face forward 1/8â€? and then pull the buttons loose at angle (pic14B).
  • 11) Set aside the faceplate and twist out all three OEM lamp assemblies with a thin blade flathead screwdriver (Note:Only a ¼ turn needed).
  • 12) Unscrew the lamp PCB that houses the lower backlighting lamp (pic15B).
  • 13) Slide internal assembly out (Pics16B&17B).

· Premium Member
1,412 Posts
Discussion Starter · #3 · (Edited)
Installing the Indicator LED lamps

If you want to change the stock LED indicator lamps that light up when a mode control button is pressed, you should do this first. They are T1 ¾ (5mm) lamps that have 2 sides shaved flat so that it resembles an oval shape (pic23B). If you measure voltage across the contact points it yields around 2vdc. This is the rating of the stock lamp. If you knew the maximum current rating (in mA), you would know exactly what parameters a replacement must be rated for or exceed. Most are rated for 2-3 milliamps so if you get a lamp whose voltage rating is more than 2v you should be fine. If you look at the circuit diagram you will see that it gets its power from the dimmer and from a 12v source originating at the Ignition “2� position. This IG2 line passes through a 5v regulator circuit on the CC board itself. The difference in these 2 supply voltages provides the lamps with enough potential to drive the lamps, yet vary in output with the dimmer and if your lights are on. You will see this dim the LEDs when you turn on your lights. When you remove the lamp from the circuit, it measures 12v. I have tested LEDs rated for 3v maximum load and they have not failed, but overdriving an LED doesn’t always mean the LED will pop. They sometimes just fail prematurely or dim over time. I had already ordered some 12v T1 LEDs (From Fry's) to replace the stock ones and they perform as good as stock (around 200mcd). If you want brighter than stock performance, go with the one I list in the parts section. My next project will test violet LEDs that are rated for 3.5v and I will update this write-up to review their performance in this circuit when that project is completed. Update: After trying the purple I believe most will find them too bright for the indicator lights without modifying the diffuser in the button. This is the thin wedge piece that is snapped into the button from the back. Take those out and sand them until rough. This should help. You may also want to use these for backlighting instead. Although not as bright as the Blue or Red, I'm sure they will be stunning. Below is a picture of the bottom of the LED enclosures that will be removed and replaced with red ones (pic19).
  • 1) You can go ahead and remove both of the stock lamp diffusers at this point (Pics18B&19B). They will not be needed. It just requires that you unscrew them from below while holding the anchor nut (pic20B).
  • 2) De-solder all stock lamp contacts (pic21B). Unclip the black plastic housing and remove the LED from it using needle-nose pliers (pic22B). If you don’t have a de-soldering bulb or iron, you can remove this by heating up the contacts while you gently pry up the clips on the LED housing.
  • 3) Slide the new LED in place making sure the Anode (+) is on the correct side marked on the housing with a “+â€? sign. Measure 8-9mm from the LED base and put a crease at that point using small needle-nose pliers. Keep in mind that the LED should sit in the housing so that it does not interfere with the button that seats up against it. To be safe, don’t have more than a millimeter or so surfacing from the inner pocket of the housing. If when you put the CC back together and the buttons do not bush back all the way you may have to trim the tiny diffuser designed for the stock LED lamps. They are clipped in, but push out from the front (pic25B). Finish bending the contacts as they were on the stock lamp, and recheck the clearance of the lamp in the housing.
  • 4) Push them into place making sure no solder is preventing the leads from going through the hole. If so (or if you didn’t remove all solder with a de-soldering bulb), just heat the points as you push the lamp stems through (pic20).
  • 5) vSolder the LED stems in place. If you need to adjust or pull the LED further into the lamp housing, use the stems to adjust the position and the solder will make this permanent when cool. You can fine-tune the position of the LED in the housing with these tools (pic26B). Just get the gap tool behind the LED and pry the lamp up or down against it using a tiny flathead. Once the LED is in place in the housing, you can now clip the length down to about 1/8â€? (pic22).
  • 6) Do this for the others and you are ready to move to the next step.

Installing the Backlighting LED lamps
This portion of the retrofit will require some trial and error fitment and focusing. The reason is that the angle of light distribution will determine the optimum placement of each LED. In relation to the button of the CC, each LED will need to be behind each one. I’ve experimented with other arrangement and this is the best method. You should familiarize yourself with the wiring harness pin-out so that you can test the backlighting before you reassemble the climate control (pics15&18). This will save you lots of agony if this is your first time with this kind of procedure. Once you choose your LEDs, be sure and test each one with the proper resistor in series so that you don’t have to troubleshoot a dead lamp once you mounted it. Also, look for substandard lamps that were shipped in the bunch and through out ones with weird color or radiant patterns. Further, test the distance needed to shine light on the entire button window. Each button has its own acrylic prism for amplifying light and they measure about 10mm across. Measure the distance your LED need to be from a surface to spread light across a 10mm box. Just draw a box on paper with the right dimensions and move the lamp back and forth until the area is filled. Mine measured about 12mm away which is roughly even with the edge of the indicator LED black housing. Another trick to minimizing intensity hotspots (and diffuse the light) is to sand and score the surface of the prism behind each button with 600grit sand paper (pics54&54B). If you have plenty of light to work with, it will not hinder the performance of the lamp much and it minimizes the need to achieve critical aiming behind the button.

  • 1) Bend and shape each LED stem/lead so that it can support itself when anchored against the grounding surface (pic23). Each lamp is wired in a parallel circuit along side the others, but it is possible to wire them in series and dial in the correct voltage with a smaller resistor, but the extra components served as anchoring devices to keep my LEDs securely mounted so I opted to wire in a 470ohm resistor for each one (pic21).
  • 2) I hot glued a single insulated copper wire to the back of the switches to provide me with a local 12v bus for each lamp to connect to. With the resistors wired in, they will provide the reach I need to get power from the bus to the LED. The Insulation was cut away at various points along the 12v bus for solder points spaced evenly behind the lamps (pics24&25). If you are careful with the lengths of the LEDs and the resistor stems they can be soldered end-to-end so that no bus is necessary and that the body of the resistor will insulate the positive current from the grounding frame it passes over (pics27B-34B)
  • 3) The side with the three buttons will need the resistors to anchor them so I hot glued them to the board.
  • 4) Now give both circuits power by running a short wire to the 12v bus on the 5-button side (the stock lamp contact furthest away is the positive one) and by reaching the center resistor on the other side to the stock lamp positive side (Closest copper contact) (pic26&30).
  • 5) Test the LED array by providing power to either Pins 6 & 13, Pins 6 and a Button frame, or clip your testers anywhere behind the resistors and to the frame (pics31,32,39,&40). If you use a red one behind the defrost button it will look like these: (pics35B-39B).
  • 6) Now clip the face onto the switches and see if any of them need any final aiming adjustments (pics41&42). Hot glue any parts/wires that may short against each other and this should be the finished product (pic35,39&43).

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1,412 Posts
Discussion Starter · #4 · (Edited)
Installing the Temp/Fan Speed Backlighting

This part of the retrofit is my solution to the fan/speed and temperature backlighting. Others have tried a neon/fluorescent lamp and driver to get some stunning super-white backlighting. Others have taken out one or both of the stock diffusers and opted for variously aimed LEDs to get the outcome they were looking for. Still others decided to keep the stock bulb behind this part of the Climate Control and call it finished. I happen to like the blue without the red part of the temperature slider lit up. It’s what happens when you put a very narrow frequency emission lamp behind a filter that filters out almost 100% of all other light. Red filters allow none of the Blue light emitted by the blue LED to come through. Some have experimented with white LEDs with good results, but they differ from incandescent lights that emit a wide band of visible light from the lamp. White LEDs often emit blue and yellow sulfides to get a very cold white. They have shown only a slight amount of Red filter illumination, so feel free to experiment with this part of the project.
You can try this yourself. Take a blue LED and fire it perpendicular to the emission surface of the diffuser from the lamp channel. The light emitting surface is the flat part that faces forward behind the slider, and the lamp channel is what I’m calling the half-circle cutout that the stock lamp is supposed to fit snuggly into. Both diffusers will slide out of their pocket and you will see that each side comes together in the middle to form a “U� shape to fit the stock lamp. I found that if you fire two lamps sideways into the diffusers that much of the light is reflected forward and focused behind the sliders. The angle here is fairly critical and when you fire one at various angles into the diffuser, you will achieve the right angle. Mark these reference angle points so that when you dremel out a channel for the LEDs to sit in, they will shine correctly into the “prism.�

  • 1) Remove the ribbon wire and lamp PCB. These are going to be replaced with a non-braided copper core wire pair. Cut about 4 inches of paired wire. Trim the positive side of the wire pair shorter so that when you solder on the resistor, it will be insulated from shorting out against the negative side. Use heat shrinking tube to insulate the resistor and that the remaining leads are stepped down to the correct voltage and just need to be soldered to the correct side of the LED array pair. See my previous write-up for calculating the resistor size. Since both of my LEDs run on 3.5 volts max, and they are running in series, the total voltage drop of the two is 7v. If the supply voltage is 13v (peak value), and the difference is 6v, you get [6/.02=300ohm]. Use the closest value. (pic57&60).
  • 2) Remove the lower large (LD) and small diffuser (SD). Just take some needle-nose pliers and grab the “toeâ€? on one end and pry from the middle with a small flat-head (pic43B&44B).
  • 3) Dremel the top LED housing. Start small and then finish to size once you’ve corrected for entry angle and depth. The dremel bits tend to melt the acrylic as it cuts so be careful about how much melted material collects on the bit or it will harden enough to cut as it get flung around in there. Take breaks to clean off the cutting bit with an exacto-knife. Having a high-speed drill press would be great as long as the bit used isn’t aggressive (pics06,51,45B). At this time, you can cut channels into the sides and back of the SD & LD to squeeze the 3mm LED stems into so that they stay in place (pic46B).
  • 4) You should now black out the end of both diffusers so that the Red LED on the LD doesn’t bleed into the SD area (pics47B). Let it dry. Slide the 3mm LEDs into the small cutout below the ones you just Dremeled out.
  • 5) Wire everything together (pic48B). Check that everything lights up (pic47B). In theory, the red LED should be biased to the area closer to where it sits. You can check this by lifting up the LD when it’s lifted and check the output to the bottom. Mine could have been aimed down more, but it’s good in person (pic49B).
  • 6) Test the output with the faceplate on (pic51B,54,55, &56).
  • 7) In-car test. Follow the first part in reverse order to install the CC back in the car (pics61-63&52B).

Author and Copyright ©: Patrick Barrera (Screen name “pIOUs�).

  • At least 15 LEDs From:
    Part # - 500TB4DF
    Super Blue
    (60 Deg.): 1,800 mcd luminosity; T1 3/4 water clear 5mm blue led lamp; forward voltage of 3.5V is recommended. [15 pieces $20.25]
    Amazingly enough, I liked these the best. With as wide an angle as they have, their output is near identicle to the 30deg bright one. I recommend them but they're out at the time of this post.
  • NEW From:
    Part # - 800TB4D
    Big Super Blue
    (45 Deg.): 3500mcd Water Clear Lens 8mm ,WOW. (470nm)
    ($1.42 each)
    These should be great for parking lights.
  • NEW from:
    Part# N500TBR4D
    Mega-Bright Bicolor
    Blue (3,000 mcd) / Red (4,800 mcd) LED in a 5mm.
    THese would be great for a multicolor setup for those who can't decide which color they like. These are the first multi-color I've seen that combine blue and red in the same LED.

· Wow! Look at that
1,118 Posts
Wow Very nice write up; I know some one who got a lifetime membership.
You got to let me look at this at the next prelude meet.
pIOUs said:
Upon review of the write-up, some of you will prefer to hire someone who has done this already to do his or her retrofit.
How much would you charge to do everything climate control, clock, ect.

· Retired, sorta
6,475 Posts
it's about time u posted it here ;)

great write up, this would've definately saved me a lot of r&d if u had done one before :p

godfather, malken claims that the offer for free membership is over already.. =-(

· Registered
424 Posts
here is a website where you can get DIRT cheap LEDS

(i did not recieve consent to advertise this website, nor am i in any way affliated with ExaByteSystems, i am merely here to share my knowledge so others may benefit)

the angle on these leds is at best minimal, and are far lower then what pious used in his write up, but the luminosity far exceeds that of the LEDS that pious used...

you can purchase them in any color, and between 3mm and 5mm in size, and almost all of the cost $0.50 each! they even have white!

· Premium Member
1,412 Posts
Discussion Starter · #16 · (Edited)
krnnamja83 said:

the angle on these leds is at best minimal, and are far lower then what pious used in his write up, but the luminosity far exceeds that of the LEDS that pious used...

you can purchase them in any color, and between 3mm and 5mm in size, and almost all of the cost $0.50 each! they even have white!
They do have good prices, but I don't like that they skimp out on the specs. The sites I listed did a good job of this and when I tested them, they performed as advertised. I'll always try new places since some of these sources have dried up after posting a writeup on another board. The flip side is that people also bring their own sources which is great. Some LED projects don't require the tolerances I list here, but these are the minimum angles (30) and the luminosity is on the really high side (it lights up my face:D ), not distracting over time. I will migrate pictures from the photo album over later so that some of you won't need to become members of imagestation.


· Wow! Look at that
1,118 Posts
^^^^ Me too.

· Premium Member
1,412 Posts
Discussion Starter · #20 ·
krayzieLuDeR501 said:
how much pious to have you do the conversion for me??
Please PM me to discuss quotes. I charge a fair price for the method described here. You can use the writeup to DIY, or as many may's too much effort. This isn't an ad for a service I provide for business, but I have done several for people who want this done badly, but don't have the skill or the tools to DIY. As for not having the time...well, that's the same reason I have to charge for the work. I do love my weekends, and my efforts have shifted toward my HID project lately. Even that is on hold for my upcoming wedding:eek: :bigthumb:
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