Headlamp relay

Dear All,

I know that one way of improving the performance of the headlamp is to fit a relay so that there is a direct feed to the headlamp and not through the switchgear. Does anyone have a wiring diagram how to do this?

Thanks in advance



Use the circuit diagram for your starter motor. The starter motor is your bulb. The starter button is your light switch.

This is what I did with mine

Wires from R to L

Headlight relay
White wire from switch to turn lights on (switch earths this)
Red/Black wire power from fuse box (+ve)
Brown wire to main/dip relay

Main/Dip relay
Pink wire from dip switch (switch earths this)
Brown wire power from headlamp relay (+ve)
Green wire to dip beam
Brown wire to main beam   Â

Brian used to have a thread on here about it on here, you will have to trawl the technical section if this does not suffice. (Ignore the word horn at the bottom)

Blimey! Having trouble following that… and look like ‘special’ relays

I can tell you how the Sprint fairing does its twin H4 headlamps…

High current earth wire (black) from battery minus terminal to headlamp(s) ground (earth).

High current supply wire (red) from battery plus terminal, with integral fuse(!), to both pins ‘30’ of two high power automotive relays.

Both pins ‘85’ to lamp(s) earth (black wire from battery).

For the dip relay, pin ‘87’ to dip beam filament and pin ‘86’ to dip switch, dip position.

For the high beam relay, pin ‘87’ to high beam filament, and pin ‘86’ to dip switch, high position. Often this is also connected to headlamp flasher button.


Note the Sprint design assumes that the relays replace the original headlamp bulb as far as the dip switch is concerned, i.e. outputs of the dip switch work exactly the same, so no modifications to original wiring.

PS: be aware that both relays pins ‘30’ are permanently ‘live’ (battery positive) so will attract corrosion. So apply WD40 generously.


Not special relays at all. I have two switches on my handlebars, on the right side the switch turns the lights on and off and is wired to the headlight relay, this is a standard 4 pin relay the type that when the current passes through the coil the contacts close and headlight turns on, it is an NO (normal open) relay.

On the left handlebar is the dip switch wired to the main/dip relay, this is a standard 5 pin relay the type that when the current passes through the coil the contacts swap from one circuit to the other (main to dip) it is a CO (change over) or DT (double throw) relay.

If you understand how relays work then it is quite easy to follow, I use a 4 pin relay to turn the headlight on and a 5 pin relay to switch between main and dip beams, Â some further reading below.


With my set up the relays are only live when the ignition is on, as the live feed is not taken direct from the battery but from the fusebox. It has the advantage of low current through the handlebar switches but does mean that there is still high current through the ignition switch. I prefer it this way as I like to turn everything off when I remove the keys. I have parking lights which can be on with the ignition key in a third position but rarely use these apart from MOT time.

LOL OK I think we’re just confusing Martin. If I get a minute I could produce a complete wiring diagram.Â