Headlight Relay Modification - NC30

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Headlight Relay Modification


Your headlights only work on full beam, and the selector button is stuck on your switchgear. You’ve taken the switch apart and repaired the problem (after losing the spring in the switch!). So how do you stop it from happening again?

The Japanese spec. NC30 uses 60/35 headlight bulbs - in other words the lighting system draws enough current to light two 35W low beam filaments, or two 60W high beam filaments. However, it is highly likely that the average owner will have had to replace their Japanese bulbs and there will have only been one choice, UK spec H4 60/55’s. However, by using two 55W low beam filaments you nearly double the current passing through the low beam contacts in the light switch, and, since it wasn’t designed to cope with this excess current, the switch melts.

So, you need to install one - but how?
Well it is pretty simple………………

Tools you will need:

  • Small flat bladed precision screwdriver (1.4mm)

  • Soldering iron

  • Wire stripper/crimper or pliers

  • Male and female blade connectors (make sure you use insulated ones)

  • 1m of 28/0.3 (min) or equivalent insulated cable

  • 1 x 20amp 4 blade relay

1. remove the left hand mid fairing and trace the wiring from the handlebar switch to a twin connector secured to the bracket holding the frame earth and top radiator stay – the connectors should be covered with a rubber boot to stop moisture and road crud getting in. Disconnect the brown and black connectors.

2. The Haynes manual has a wiring diagram in it that includes a low beam relay (this was only installed on UK models). You are trying to mimick this set-up. Basically the white wire that supplies current to the lights goes straight through the light switch on Japanese models, and this needs to be cut to allow the handlebar switch to power the low current side of the relay you’re about to install. However, this is the only wire that needs to be cut; the others can be taken out of the connector, joined with solder and replaced. To take them out you will need the smallest flat bladed screwdriver in a normal precision set (i.e. 1.4mm); push this into the pin in the connector (not the side the wire goes in) until it clicks the retaining clip out of the connector, and remove.

3. Cut three 100mm lengths of wire and strip back 10mmm of insulation from one end of each. These will be soldered onto the block connector pins. The trick is to expose enough wire to allow the connection to be made and insulated with a couple of turns of tape without it becoming too thick and therefore impossible to re-insert into the connector block.

4. Be sure that you are working on the connector blocks attached to the wiring harness, not the handlebar switch. Remove the black/red pin from the brown block and solder one of the wires to it (see step 2). Do the same with the green wire running to the black block (N.B. the black block is shown as green in my Haynes wiring diagram). Insulate the connections and replace them in the connector blocks.

5. Solder a wire to the white pin in the brown block. Insulate, then replace the pin into the block. Then cut the white wire allowing enough room to connect a female blade connector to the lighting side, and a male blade connector to the connector block side. Insulate the male blade as this is not needed to install the relay, it is simply a neat way of allowing the wiring to be re connected as the Japanese intended (should the need arise?!).

6. Trim the wires to a suitable length (depending where you will be locating the relay). Remove about 5mm of insulation from the end of each wire and crimp a male blade connector to each. Cut a further 100mm of wire and crimp another male blade to both ends. Connect this to the exposed blade on the end of the white wire that runs back to the lights.

7. Connect each of the wires to a terminal on the relay as follows:

  • 30 – black/red (power)

  • 85 – green (earth)

  • 86 – white - from switch

  • 87 – white - to lighting (i.e. the wire with crimped connectors at both ends)

8.Replace the black and brown connectors and pull the boot down as far as possible. The relay I used was too big to push up into the boot so I cable tied it in place and sprayed it with damp start silicon spray. A more permanent solution might involve a blob of araldite. Just make sure it sits with the cables pointing down or water will get inside it. Turn on the power and try the lights! You should hear a click from the relay when you switch to low beam, and of course both lights should work.

If they don’t, check all the connections you made and retry.

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