Switch for Single-Headlight-Off - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 5 Old 12-21-2006, 06:44 AM Thread Starter
Join Date: Jul 2006
Posts: 180
Switch for Single-Headlight-Off

A little while ago, in order to provide more electrical power for my Gerbings jacket liner and heater grips, I followed the logical suggestions that I had read here about turning off one headlight via a switch. Because my morning commute is always in the dark (58 miles one way), I use my high beam quite a bit. Accordingly, I reasoned that the sensible way to wire in a switch was to connect it to the right headlight's ground wire. Then, when I turn off the switch, I remove the ground and the right headlight should go off. In reality, when I turn off the switch the right headlight does not go completely out, but instead only gets quite a bit dimmer.

I figure the only way this can happen is that 1) the switch is not breaking contact 100%, or 2) the right headlight bulb is somehow alternately and partially grounded.

Any electrical gurus with any input on this?
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post #2 of 5 Old 12-21-2006, 08:21 AM
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Originally Posted by rotorhead View Post
Any electrical gurus with any input on this?
Putting the switch in the hot leads is the right way to wire it. What you're seeing is stray current flow through the low and hi beam filament since you've lifted the ground.

In this particular case, you have a hot lead for each filament in the lamp. Use a two pole switch to switch them both at once. That'd be a DPST switch in techie parlance (double pole, single throw). DPDT can also be used (double pole, double throw).

-Tom (DL650AL2) (KA1TOX) (E-I-E-I-O)

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post #3 of 5 Old 12-21-2006, 08:25 AM
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Always kill the power, never the ground. Cutting ground on anything electric can do weird, unpredictable stuff, also it is dangerous. Rewire that thing ASAP before you damage something.

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post #4 of 5 Old 12-21-2006, 08:31 AM
Join Date: Dec 2006
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Correct answer is 2). The R headlight's low beam has a connection to ground via the high beam wiring. Take a look at the wiring digaram below.
B/W = "-"
Y = "High beam +"
B/Bl = "Low beam +"


When the ground of R headlight is open the current from R low beam travels through R high beam filament to L high beam filament and from there to ground.

To cut-off one of the headlights you do need to cut the "+" connection.

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post #5 of 5 Old 12-21-2006, 08:41 AM Thread Starter
Join Date: Jul 2006
Posts: 180
Thumbs up

Guys - I appreciate the quick replies, that makes perfect sense once it was laid out for me. I'll get a DPST or DPDT switch and wire it in to the positive leads ASAP.

Thanks a bunch!
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