With this guide I'm going to show you how to replace the stock bulb lights inside the dash of a Suzuki with white leds. In my case the problem with stock lights were false contacts between lights and the pcb inside the dash, so while riding the main back lights kept turn on and off randomly along with the vibrations from the bike. So why just repairing the false contacts if I can swap the bulbs with leds? Here we go...
when doing the electrical calculations in the next steps, I didn't take in consideration that when the engine is running the power source is roughly 15-16V and not the 12V from the battery. This because the 15-16V coming from the regulator is needed to charge up the battery.
This is very important because with 16V and the 330ohm resistor our white led (3.5 forward voltage) would drain (12.5V / 330 ohm) = 0,037A = 37mA which are too much! the led would burn almost instantly. Use a 500 ohm resistor to be safe: this way the led will draw (12.5V / 500 ohm) = 0,025mA which are perfect.
Calculations updated in the relative step.
Step 1: List of Materials
In order to make our mod we need these materials:
- 3 white diffused leds - if you just have the clear ones i'll teach you a trick to get them diffused ;)
- 3 x 500 ohm resistors 1/2W
- thin cables
- soldering iron and tin solder
- 1mm or 2mm drill bit (2.5mm is too big, so don't exceed the 2mm)
- screwdrivers and wrenches to get the dash out of the bike
Step 2: Get the Dash Out
In order to get the dash out of the bike we need to
- unplug the battery (to void any damage)
- remove the windscreen: 4 screws in the front and 2 in the back next to the rear mirrors
- remove the 3 screws that hold the dash from the front
- remove the front dash cover
- unplug the connector from the dash
- now the tricky part: remove the 4 bolts that hold the dash from behind (you're gonna need an 8mm wrench). There are two bolts on the left side, one in the middle right under the socket and one in the right side. Unfortunately it was impossible to show them all with a picture because two of them are hidden, but with a light you can at least see where to put the wrench in order to unscrew the bolts. In the last picture you can see where are placed the 4 bolts in the back of the dash.
- now you can remove the dash
Step 3: Open Up the Dash and Resistor Calculations
open up the dash by removing all the screws that you can find in its back. You should spot the grey plugs that contain the bulbs that we have to swap with leds.
The 5mm leds have the same size of the bulbs, so that's great! The main problem with my leds is that they are clear and the light angle is 30° which isn't good: if you place this type of led you won't get any diffused light in the dash but you will create and uneven brightness with 3 circular lit spots leaving all that remains in the shadow. What you want to get are diffused leds or do just like i did: scratch the surface of the leds with a medium grit sand paper until you get an even white surface! Now you have nice diffused leds. Cool uh?!
Now some electronics:
We have a power source of 15-16V (from the regulator), the forward voltage of white leds is 3.5V and the typical led current draw is 20mA (0.02A) but we can push the value up to 25mA to get a brighter illumination, so we have to place a resistor to compensate that (16V - 3.5V) = 12.5V. The correct value of the resistor, so that the led can draw exactly 25ma, would be (12.5V / 0.025A) = 500ohm. Now the power consumption of the resistor would be (12.5V * 0,025A) = 0.31W, so a 1/2W resistor type is perfect.
By replacing the bulbs with leds the power consumption will drop down from 6W to 1W (3 x 0.17W) saving a lot of power.
Step 4: Swapping the Bulb With the Led
take the grey plug and by removing the bulb you'll notice the copper contacts at the inside. Now since i have false contacts between those contacts and the pcb i had to take a drastic decision: bypass those contacts by making some cable connections (mainly because this is the 2° time i open up the dash, and in the first attempt even if i cleaned up everything and scraped all the contacts from dirt it didn't solve the false contact issue). If you don't have those problems you should bypass the next two initial steps.
- remove the copper contacts from the grey plug
- drill 2 separate holes with a 1mm or 2mm bit inside the plug
- take the resistor, bend one side to 90° and put the main body of the resistor between the led pins placing the bended side onto the negative pin of the led (the shortest one)
- solder the joint between the resistor and the led, and trim the excess (led and resistor must be in series and not in parallel)
- now you can insert the led+resistor inside the grey plug so that the pins come out from the drilled holes, and finally bend the pins on the plug. (if you haven't any false contact problem then you just have to solder the pins on each copper contacts inside the grey plug, and you're ready to go. Before rebuilding everything up be sure that each led lights up, and if this is not the case just turn to 180° the grey plug on the pcb: leds have a 'direction', so if you plug them the wrong way you won't damage anything, but they won't light up either)
Step 5: Modding the Pcb
This step is a guide to bypass the stock contacts between grey plugs and the pcb traces, and it's needed if you have false contacts just like me. From now on i can't take any responsability for what you are doing: you're modding the heart of the speedometer, so double check everything before making any terrible mistake and if you're not confident with a soldering iron i suggest to not keep on going with the next steps because you can compromise your dashboard. That said, we need the multimeter to try to understand how are disposed the traces on the pcb in order to bypass the stock contacts by soldering the thin cables in the first near spots available. If you follow the traces with the meter, you're gonna find out that all the 3 lights are 'wired' in parallel, so there is a common ground for each light as well as a common 15-16V source. What we have to do now is to recognize the ground traces and the 15V traces.
i found out the common traces, and to make the job cleaner i soldered a red cable to the 15V source traces and a black cable to the ground traces. In the pics you can see for each light where to solder the cables (if you're not sure just check the continuity with the multimeter). Finally put the grey plugs back in place and solder each red wire to the led pin (easy to spot since it's thicker than the resistor pin), and each black wire to the relative resistor pin. Before hooking it up to the connector from the bike double check all the soldering joints you made voiding any kind of short. Now close the dash and plug the connector from the bike to test the leds.
Enjoy your brand new dashboard and drive safely.