Rewiring for Aftermarket (Xenon/HID) Headlights - Most bikes

Your stock headlights just never seem bright enough do they?
Pathetically designed Standards laid down by the government, and manufacturers trying to save every single paisa to just meet the regulations (not exceed them to ensure customer safety). Sad

The answer: a headlight upgrade. HID, LED or Xenon, keep the stock reflector or switch to projector.
I do not have before and after photos on my bike, but here’s a link to a similar article on another site.
Cyclops LED Headlight Bulbs Let You Conquer the Night - ADV Pulse. While the entire article is a good read, I mainly want to draw your attention to the photographs that show a clear difference between the stock and aftermarket headlight bulbs.


This is my guide on how to rewire the headlight wiring to ensure that your new headlight operates properly, and lasts longer.
PM me if you have any problems understanding the instructions, and I will try to recreate some of the steps for photographs if the explanation provided is not very clear.

Level – Requires moderate skill in soldering. Shouldn’t take more than a couple hours.


Requirements:
Your new headlight
12V relay (Maybe. I will come to that)
Moderate soldering skills
A willingness to mess with your vehicle’s electronics

Tools:
Spanners and Screwdrivers, as per vehicle requirement
Soldering Iron, flux and Solder (recommended)
Wire strippers (I prefer nail cutters)
Insulation tape or heat-shrink tubing
Multimeter helps if you know how to use the continuity function

Step 1: Access your headlight bulb
Steps and tools for this are entirely vehicle specific. I think most owners manuals also do not give instructions for it, so best to ask a mechanic for help if you are having troubles. Alternately, PM me, and if I have access to the vehicle, I could explain the steps.
When you get to your bulb, you need to identify it. This is easier said than done if there is no marking. Normally, the front of the base will have details of the type, voltage, wattage, etc. Most motorcycles use a bulb type that is called HS1. The telling features of this are
1) There will be 3 alignment pins coming out of the side of the base, where 1 will be wider than the other 2.
2) There will be 3 terminal pins sticking out of the back for connections
3) The bulb will have 2 filaments, where the front filament will have a small reflector below it.


If your bulb qualifies the above criteria, it is HS1, and we can proceed. The aftermarket bulbs available in India are almost exclusively H4 type. The good thing is that a H4 bulb will fit into a HS1 socket without too much fuss, but the other way round is more difficult. The wiring is slightly different in that you can replace a HS1 with H4, and it will work, but for sustained use, you will have to make some modifications to the wiring.

Step 2: Rewiring
HS1 and H4 have the wiring reversed for the High and Low beams. This means that when you connect an aftermarket H4 bulb to stock wiring, the bulb will be in High beam when switch is in Low beam, and vice versa. Also, since the wiring is reversed, the passing switch will activate your Low beams (not High beams)


Correcting this is nothing complicated. First, disconnect the wire running from the Wiring harness coupler to the bulb. The same wire may also be connected to winkers, pilot lamps, etc. Disconnect all the couplers so that you can work on the wire easily. The wires will be colour coded for easy reassembly, but better to make note of what goes where.
Cut the 2 wires (mostly White for low beam and Blue for high beam). Reconnect them the other way around (White to Blue, Blue to White)
Soldering is recommended, followed by insulation using tape or heat-shrink tubing.



Step 3: Replace the Bulb
Insert the new bulb in the socket and fasten it the same way that the stock bulb was held in place. There may be some instances where there will be a protrusion in the socket to prevent ‘accidental fitment’ of a H4 bulb into the HS1 socket. This can be filed off or snapped off using a pair of pliers. Then the bulb will fit properly.
Many bulbs also come with multiple backing plates (see the photo of the kit below) so that you can pick one that matches your socket. Choose the one that looks like what the stock bulb uses.

Step 4: Reconnect the wiring, reassemble and done
Quite self explanatory right?

Note: The Step 2 above holds good if you are replacing the stock bulb with another bulb. If you choose to replace it with Xenon lamps or projectors(which also come with Xenon lamp inside), then the steps are a little different.
While the stock halogen bulb or HID bulb operates on the principle of heating a wire till it gets so hot that it emits light, Xenon bulbs work by sustaining an arc. Ever seen anyone welding and noticed how bright the light was? Xenons work in the same way, but with a smaller and more controlled arc. So to ignite the arc, you need several thousand Volts for a few milliseconds, then a sustained voltage of around 80V, but at a lower current than halogen bulbs.
This big opening voltage and the sustained higher voltage is provided by a system called a ballast, that comes along with the lamp. So instead of re-wiring the coupler, we will take the supply from the wires, and connect it to the ballast. The ballast normally comes with a length of wire that is open at one end so that it can be connected wherever necessary. Below is the kit that I bought from MXS Motorsports on ebay (This is not product placement. The photo is watermarked, so I decided to be upfront about it.)


Although we are connecting H4 to HS1, Blue goes to Blue, and White to White (High beam signal should go to High beam input, and Low beam to Low beam). Green goes to Green. You can cut off the bulb coupler if you want (Variant 1), but I decided to keep it (Variant 2). Advantage of Variant 2 is that if and when the Xenon fails, you can always reconnect the stock bulb till you get a replacement Xenon.



There is 1 more important characteristic that distinguishes Xenon lamps from Halogens.
Halogens have dual filaments. When you put the headlight switch into Low beam, the Low beam filament lights up. When you put it into High beam, the High beam filament lights up. When you put it into Low beam and press the passing switch, both filaments light up.
Xenon lamps have 1 set of electrodes, hence 1 arc. To compensate for High and Low beams, a Xenon lamp has a solenoid. In a reflector style setup, the solenoid moves the electrodes into the High beam and Low Beam positions as per the position on the switch. In projectors, there is a blocker plate that moves to control the light flow.



Bottom line is that if the headlight switch is in Low beam or High beam position, there is only 1 signal going to the lamp (stay in Low beam position or stay in High beam position). But if the switch is in Low beam position, and you press the passing switch, you are sending 2 contradictory signals (the xenon lamp can be either in Low or High position. Not in both, like you are asking it to).
To address the above issue, we need to add a relay. The job of the relay is to disconnect the Low beam signal whenever a High beam signal is activated (either through the dipper switch, or passing switch). This way, when you get a High beam signal, the Low beam signal is automatically cut off by the relay.


The relay we will be using is commonly called a ‘sugar cube’ relay, owing to its size and shape.
The relay has 5 terminals – COM (input), NO(output 1 that is normally disconnected, connects when relay is activated), NC (output 2 that is normally connected, gets disconnected when relay is activated). The other 2 terminals are for the relay coil from where the relay is activated. They work the same way either way you connect them.


I am not sure which is NC and which is NO (what I think it is is marked in bold), but better to check with a multimeter. Put the multimeter into the continuity function and touch 1 probe to the COM pin. Take turns touching the 2^nd probe to the opposite 2 pins. The pin on which the multimeter beeps is the NC, and the pin on which it does not beep is NO. Better to make a note of the pins once you find which is which.

For the application we require, the High Beam wire (Blue) will be cut and the 2 ends will be soldered to the Relay coil pins. The Low beam wire (White) will be cut and one end will be soldered to the COM pin, and the other to the NC pin.




This way, the Low beam connection is normally connected for the Low beam usage, but when the High beam is applied, the current flowing to the ballast flows through the relay coil and activates it, thereby disconnecting the Low Beam.


Complicated stuff. My headlight wire has been cut and re-soldered 5-6 times during my ‘learning’ (hit and trial) process. What a mess it is. Got my hands on a new headlight wire, so will upload pics when I redo the job.

So enjoy your modding, and PM me if you need any help. I’ve got quite a slew of mods to go along this one.
USB charger
Custom design DRL
Rewiring switch cluster so that DRL are always on and you free up 1 spot on the switch for additional lighting/accessory control
Helmet holder off the back of the bike
LED winkers
Reflective graphics
… just to name a few.

Attached Images