making a headlight switch?
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=133078
Printed Date: July 12, 2025 at 8:12 PM
Topic: making a headlight switch?
Posted By: orangesuburban
Subject: making a headlight switch?
Date Posted: December 25, 2012 at 7:55 AM
I'm redoing the controls on my bike and have to make the headlight hi/lo switch, my only option is to use an on/off switch to control hi/lo on h4 bulbs. Is there a way I can put a relay inline with the switch so when I turn the switch "on" it will cut off power to the low beams and send power to the high beams? Powering both beams at the same time is not an option.
Thanks.
Replies:
Posted By: i am an idiot
Date Posted: December 25, 2012 at 9:49 AM
Using a relay, connect switch controlled power to terminal 86, ground terminal 85. Fused switched power to terminal 30, low beam to terminal 87A. High beam to terminal 87.
The first mentioned switched power is from the switch to switch low to high. The second mentioned is ignition switch controlled.
Posted By: kreg357
Date Posted: December 25, 2012 at 10:09 AM
Here is one way to do it.
Assuming the Low Beam Headlights will be ON while the bike is running...
Wire 30/40 Amp ( weather sealed ) SPDT relay as follows :
Pin 85 to ON/OFF switch to chassis ground
Pin 86 and 30 to +12V Ignition switched power
Pin 87A to Low Beam
Pin 87 to High Beam
Switch OFF will be Low Beams. Switch ON will be High Beams.
Diagram below :
 ------------- Soldering is fun!
Posted By: kreg357
Date Posted: December 25, 2012 at 10:10 AM
Slow making picture but Mr. I, we think the same.... ------------- Soldering is fun!
Posted By: orangesuburban
Date Posted: December 25, 2012 at 1:34 PM
Awesome, thanks guys!!!
Posted By: orangesuburban
Date Posted: December 25, 2012 at 9:45 PM
kreg357 wrote:
Didn't work.
Blows a fuse every time I throw the switch. Double checked and I have it wired as shown.
Posted By: i am an idiot
Date Posted: December 25, 2012 at 10:08 PM
If that blows the fuse when you hit the switch, the high beam wire is shorted to ground.
Posted By: orangesuburban
Date Posted: December 26, 2012 at 7:07 AM
The way I wired it for clarification
86 jumped to 30 then to bike headlight power wire
87 to high beam
87a to low beam
85 to one leg of switch, other leg of switch to ground.
----
The OEM switch which I am trying to remove in lieu of this new switch is
single power wire
switch toggles power from going to low beam wire or high beam wire.
Posted By: i am an idiot
Date Posted: December 26, 2012 at 1:52 PM
If the low beam works, and it blows the fuse when switched to high beam, there has to be a short from the high beam wire to ground.
Posted By: orangesuburban
Date Posted: December 26, 2012 at 2:07 PM
i am an idiot wrote:
If the low beam works, and it blows the fuse when switched to high beam, there has to be a short from the high beam wire to ground.
I can power the high beam without the relay and it works fine. I can even power both low and high at the same time without relay and no blown fuse.
bad relay?
Posted By: orangesuburban
Date Posted: December 26, 2012 at 2:14 PM
Just found this online I will try tonight, how does it look?
incase pic doesnt work:
87 to high beam bulb
87a to low beam bulb
86 to ground
85 to one leg of switch
30 to other leg of switch and head light power wire.
Posted By: i am an idiot
Date Posted: December 26, 2012 at 9:30 PM
The only thing I can think is there is a diode internal of the relay. I know that 85 should be ground, and 86 should be positive in voltage. So if there is an internal diode, since the above is the standard, I would imagine the internal diode would be correct. However, this is the only thing I can see. Try power to 30 and 85, then ground 86 through the switch.
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