Introduction

This modification can be done without running any new wires (long ones, anyway). The left-hand side middle and lower fairings will need to be removed, because the access point is a set of connectors on the lower left-hand side of the bike. You'll need basic electrical tools to do the mod. Secured in a metal bracket are two six-pin connectors (each with only five wires) covered by a PVC hood. Once the wiring is completed, it is possible to push the relay up inside the hood "up-stream" of the connectors, so everything remains more or less protected from the elements.

UK-spec NC30s came with low beam relays and 55/60w H4 headlight bulbs as standard. Essentially, this modification attempts to mimic the UK-spec headlight circuit without having to modify the bike's wiring harness. On the J-spec NC30 headlight wiring diagram to the right, the white wire goes from the low beam element on the 35/60w H4 bulbs directly to the handlebar switch. If you simply fit higher wattage bulbs without adding a relay, the switch (which is available only as part of the switch pod) will see more than 55% additional current on a repetitive basis—every time you switch the headlights on, or from "Parking" to "On."

Pull the headlamp connectors off both of the bulbs, then, using a continuity tester, find the white (ish) wire (lo beam) on one of the "up-stream" connectors. You will also need a ground—there's a black wire with a green band around it on one of the connectors that works fine (even if it may be a floating ground). Then, you will need to find the "Bat5" power lead—black with red stripe—it's the same wire that powers the hi beam relay on the other side of the bike. Wiring the relay is a matter of tapping into (without necessarily cutting) the ground and power leads (temporarily releasing the contacts from the connectors with a tiny screwdriver makes this easier) and cutting and intercepting the white (ish) lo beam lead. Note that the "hot" side of the white wire connector is the one that you are working on, i.e., the power comes from the handlebar switch and runs down and over to the other side of the bike before going back up to the headlight bulbs.

The aforementioned "standard automotive relay" has four contacts, conventionally labeled 85, 86, 87 and 30 (see the new relay in the diagram above). The contact labeled "30" is the input power (black with red stripe) lead; 85 is the ground; 86 goes to the handlebar switch; and 87 goes to the headlight bulbs. Solder and wrap all of the connections, plug in the headlight bulbs, and see if it works! If you ever want to remove the relay, make sure you use "female spade" connectors on the relay contacts; then you can quickly connect the two white (ish) wires back together, and you're back to Honda spec.

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