Headlight tuning is popular as a customization that can be both practical and stylish, and it is common to replace the bulbs with high performance and high functionality bulbs such as HID and LED. However, there is still room for improvement in the normal headlights. The key to this is to direct the ground wire.
Headlight relays are commonly used to increase the light output of stock headlights.
The harnesses for the meter, ignition switch, and left and right steering wheel switches are clustered around the headlights and tend to be crowded even in new motorcycles. In older motorcycles, the couplers and connectors are not as sophisticated as in current motorcycles, and in motorcycles that have been through many users' hands, it is common to cut and splice wires, so it is necessary to tidy up before customizing.
The fact that an electrical circuit is formed by electricity flowing from the power source to the load and then back to the power source is the same whether it is AC or DC. It also works whether the voltage is high or low. Even riders who are not very good at electricity should be able to understand this if they think of the wiring between a dry cell battery and a bean bulb.
The headlight of a motorcycle can also be basically explained by the relationship between a battery and a bean bulb. However, the wiring of a motorcycle is a little more complicated, and if the battery is used as a base point, the path is battery -> fuse box -> ignition switch -> headlight switch -> dimmer switch -> headlight bulb -> ground wire -> battery. Of these, current motorcycles do not have a headlight switch because the headlights are always on. Instead, some models have relays built in so that the lights do not come on with the key on, but only after the engine starts.
HID and LED bulbs are popular as custom parts for stock headlights that use filament bulbs. These bulbs use a mechanism such as a discharge or semiconductor instead of a coiled filament, so they consume less power than the stock bulbs and still look bright.
However, many owners of out-of-print and older motorcycles don't like the look and feel of modern headlight bulbs, which are very different from bulbs. Nevertheless, bright is always better than dark, which is why some riders install headlight relays to shortcut the long journey from battery to headlight bulb. Headlight relays make a lot of sense in that they use the current flowing through the ignition switch or dimmer switch to signal the relay, thus eliminating the electrical losses that occur gradually over a number of contacts.
However, in order to incorporate the headlight relays, space is required to fit the relays, fuses and other components. A relay that directs the current from the battery to the headlight bulb is required for each of the low and high beams, so at least two additional relays must be fitted. In the past, many headlight relays were designed to be mounted in the headlight case or under the fuel tank, which could be a challenge on naked-type models.
Some products are sold with relays located on the side covers or near the battery to avoid congestion in the headlight case, but not all current motorcycles are easy to add relays to, due to the efficient placement of necessary components in limited space.
- Point 1 - The wiring that leads from the battery to the headlight bulb has a number of contacts along the way.
- Point 2 - If you equip a headlight relay, you can reduce the loss at the switch, but you will need space to add the relay.
Many of the ground wires are tachometer wires and don't go back to the battery!
The image shows a different scooter from the Kawasaki Z1-R, where a new ground wire is being installed. The green ground wire from the electrical components of the motorcycle is fixed to the frame. On the other hand, the thick earth wire leading to the negative terminal of the battery also passes through the negative terminal of the starter motor and connects to the frame, where it is tightened together with the green earth wire. Theoretically, the circuit is formed by body grounding, but considering the fact that the green ground wire has many branches on the way to this point, it is easy to imagine that direct grounding from the headlight bulb would have a smoother flow.
I'm pretty sure the headlight relays make the stock headlight bulbs brighter. There's room for improvement in the stock harness. The side that goes from the positive side of the battery, through the key cylinder or dimmer switch, into the headlight bulb, stays the same. What I'm looking at is the ground wire on the exit side from the valve back to the negative of the battery
The electricity that enters the electrical components of each part of the motorcycle follows various paths, but after passing through the electrical components, it all returns to the negative side of the battery. For this reason, in order to reduce weight and cost, the stock harness has a ground wire connected to the main ground wire like a branch from each electrical component. Depending on the model, they may be grouped by function such as lights or fuel, or all together, but with the exception of the starter motor ground wire, it is unlikely that each ground wire from each electrical component returns to the negative side of the battery independently.
On top of that, it's important to note where the ground wire goes. Nearly all motorcycles have the ground wire connected to the crankcase or frame of the engine, not the negative terminal of the battery. And the negative battery wire is also connected to the crankcase or frame. Since both the crankcase and the frame are conductive metals, the circuit is established by the so-called frame ground.
A typical circuit tester like the one we have will show zero resistance connected to the crankcase with many ground wires repeatedly merging. However ...If the current becomes large, thin wiring with many connections will cause resistance. The reason why only the wiring between the battery and the cell motor is extremely thick in motorcycle wiring is to allow the high current consumed by the cell motor to flow without resistance. The reason why only the wiring connecting the battery and the cell motor is extremely thick in the wiring of the motorcycle is to flow the large current consumed by the cell motor without resistance. Although the headlight is not as large as the cell motor, the H4 bulb is 55/It has a power consumption of 60W, and more current is flowing than other electrical components.
The size of the wiring used in the factory harness is sufficient for the power consumption of each electrical component, but it is also true that thicker wiring will allow the electricity to flow more smoothly. On the entrance side from the battery to the headlight bulb, there are a number of switches and contacts such as the ignition switch and dimmer switch, so it is not easy to make the wiring thicker. However, if it's a ground wire, it's easy because it's just a straight line back from the headlight coupler terminal to the negative terminal on the battery.
- Point 1 - The ground wire after passing through the electrical components of each part of the motorcycle's body, the wiring of each part of the motorcycle's body is put together.
- Point 2 - The ground wire is not directly connected to the negative terminal of the battery, but is the body ground through the engine and frame.
The older the motorcycles, the more effective the ground wire return.
To improve the flow of electricity without the headlight relay, only the headlight ground wire is independent. It's like a more direct approach to Earthing.
The left is the stock ground wire and the right is the new wire. The stock size wire is sufficient for the overall power consumption of the motorcycle, but if the main line is interrupted by branch wires from here and there, and the connections are corroded over time, the resistance may increase. The resistance of the stock ground wire is zero when measured with a circuit tester, but when the current flow is measured, more current will flow if a dedicated ground wire is added.
Simply unplug the stock terminal from the headlight coupler and insert the terminal with the thick new wire cupped to it to complete the ground wire. Pull it up to the battery so that it crawls over the stock harness, caulk the round terminal, and cotighten it to the battery terminal.
For the ground wire from the headlight coupler back to the battery, use a thicker cord than stock. Here we will use a thicker heat resistant vinyl wire called 3.5sq. The general wiring is about 0.75sq, so it is quite thick. By the way, the allowable current of the 3.5sq wire I had on hand is 39A, which is more than 450W if the voltage is 12V, which can be called over-spec.
I replaced the stock ground wire with this wire and connected it directly to the minus terminal of the battery terminal, and the amount of light definitely increased over the stock ground wire. There are many harnesses of old motorcycles and out-of-print motorcycles where oxidation has progressed on both the plus side and the ground side, and in many cases, oxidation has occurred on the ground side at the solder and clamps when the branches of each electrical component connect to the trunk.
The more that is the case, the more pronounced the effect of the direct ground wire will be. It is much slimmer than adding a headlight relay, although it will increase the size of the new wire. Even if you don't decide to do it permanently from the beginning, you can connect it from the headlight coupler to the battery minus tentatively and feel the difference in brightness before wiring it.
Here we put the ground wire back in on a Kawasaki Z1-R and could see a clear difference as the stock harness had deteriorated to match the age of the motorcycle. Without replacing the headlight bulbs with the latest trendy parts, and without adding headlight relays, the direct ground wire can brighten up the headlight by making the flow of electricity smoother than it is now.
The difference is clear in the picture even though I did not modify the entrance side from the battery positive to the headlight bulb and just replaced the ground wire on the exit side. With the human eye, the ground wire effect is even more apparent than in the picture. If your motorcycle has room for a headlight relay, you can choose a relay, but if you want a brighter headlight, we recommend installing a new ground wire.
- Point 1 - There is a concern that the flow of the ground wire may be blocked by connecting a number of oxidized wires due to aging.
- Point 2 - Just by adding a ground wire that connects directly between the headlight bulb coupler and the negative terminal of the battery, you can increase the light output of the headlight.
