Headlight relay question

[GWS]

Can I use a 3 pin relay to bypass the starter switch and send power directly to the headlights from the battery? I've seen a diagram using a 5 pin relay. It doesn't look too complicated, but I'm always looking for a simpler way.
Thanks.

[MarkT]

Yes but 3-pin is not simpler than 5-pin.  3-pin you have to ground the case which may or may not involve a 4th wire depending on where & how you mount it.  Placed in the bucket you are depending on ground current to make it reliably through the fork bearings.  I always buy 5-pin relays as they are more versatile when you need the 87a pin (normally on), and I ground all relays anyway.  I'm not referring to the 5-pin relays with two 87 pins which replace a Y-yoke for powering two devices like spots.

[GWS]

Good to know. Thanks. 

So on a 5 pin relay:
85 goes to ground,
86 takes the blue/white wire coming in from the starter switch,
87 takes the same blue/white wire going back out to the hi/low switch,
Then I run a wire from the 30 pin and cut it into the wire running from the headlight fuse to the starter switch?
And the 87a pin goes unused?

[MarkT]

Chet Walters' graphic explaining the relay's pin use:



Correct on your pins.  Use of 85 & 86 are interchangeable.  30 is also called 51 on some relays.  It also doesn't matter which way the current goes through the relay, between 30 & 87 - they are also interchangeable.  In your case 87a is unassigned.

What I said above applies if you are wiring spots - though your connection to 30 should come from the battery via a fuse - not from a switch.  The blu-wh wire is used as a trigger and will trigger the relay when ignition is on and the start button is NOT pressed - then it goes off.  This will reduce the load on your starter switch.

HOWEVER - if you are wiring a headlight with hi-lo beams - you need a relay for each side of the headlight - one for the high beam and one for the low.  Then you cut the low beam wire and connect it to pin 30 on one relay - and reconnect the other side of that same wire to the output of the relay - pin 87.  You do the same for the high beam wire.  Obviously this is best wired with the relays IN the headlight bucket - and that's where mine are on Jade, Deerslayer and George.  I explain this in detail in http://horseapple.com/Valkyrie/Tech_Tips/Headlight_Upgrade/headlight_upgrade.html

If this is an interstate - split each output wire into a Y-yoke and run the 2nd wire over to the other headlight shell.  Just disconnect the headlight plug there, make up a plug that uses the 2 wires you are bringing over.  You don't need to have another pair of relays for the 2nd H4 bulb.  You do need to run a ground for the second light, or just replug the ground wire already there into your new H4 plug.  BTW NAPA has ceramic H4 hi-power plugs if you want to increase the wattage some w/o roasting the OEM plastic plug.