Positive Ground with Negative Ground Lights (2017)

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Is it possible to just swap the wires on the tail light so you can use a negative ground LED bulb on a positive ground bike?

Logic says the electrons won't know the difference. Experiences says to ask people smarter than me.

#askingforafriend
 
Sure. As long as the anode side is more positive than the cathode.
 
Some LEDs are available that will work with positive earth and some will work with either.
LED is the style that replaces the original filament lamp by fitting into the original holder but the holder doesn't earth through its mounting but by a wire just connect as required. My warning lamps in headlight are normal negative earth LEDs but as the holder is all plastic an connections for positive and negative feeds are by wire its no problem.
 
swooshdave said:
Is it possible to just swap the wires on the tail light so you can use a negative ground LED bulb on a positive ground bike?

Logic says the electrons won't know the difference. Experiences says to ask people smarter than me.

#askingforafriend

I've wondered about that too, and I think the problem comes down to not enough inputs if you reverse the circuit. You would connect the earth lead (red) to one of the taillight feeds, and ground the corresponding taillight lead. That would be one circuit, but where do you get the other discrete input to provide for the brake circuit. Does that make sense?
 
FWIW
All the 12v taillights I have ever seen are 1157 type bulbs. Two connections on the base, one for the running lights, one for the brake light. They ground through the base of the bulb holder. I think it would be a real PITA to get that to work correctly. I was able to find positive ground bulbs and just simply replace the bulb. My instruments have plastic bulb holders so that was a simple matter of swapping leads.
Pete
 
Won't work, not with the brake light anyway, will require rewiring of the brake switching circuit. The problem is not in the running light, but with the brake light circuit, as this is switched using the opposite circuit. I ran into this with my seat unit that has an integrated LED, I had to create a new circuit for both the front and rear brake switches using the negative side, wasn't THAT big of a deal, but a deal nonetheless

Anyway, from memory this is a diagram of the circuit I had to make up that's independent of the main harness:

Positive Ground with Negative Ground Lights (2017)
 
If the tail light housing (or the light socket) is electrically isolated from the frame (fender) then you can run wires to it for either polarity. Cuz the electrons nor the LED care what they use as a conductor so long as it makes a circuit. The polarity of the LED matters, not the circuit.

Russ
 
I am on a constant lookout for a non-polar 1157 LED bulb...no joy. Ordered some, out of China, that claimed to be non-polar but they were not. The only tungsten filament light on my bike is the tail/brake one.
Jon in SC
 
rvich said:
If the tail light housing (or the light socket) is electrically isolated from the frame (fender) then you can run wires to it for either polarity. Cuz the electrons nor the LED care what they use as a conductor so long as it makes a circuit. The polarity of the LED matters, not the circuit.

Russ

A double filiment bulb like a taillight can not be flipped that easily. The simpilist solution is to get a + earth bulb.
http://www.dynamoregulatorconversions.c ... s-shop.php

Pete
 
Deets55 said:
rvich said:
If the tail light housing (or the light socket) is electrically isolated from the frame (fender) then you can run wires to it for either polarity. Cuz the electrons nor the LED care what they use as a conductor so long as it makes a circuit. The polarity of the LED matters, not the circuit.

Russ

A double filiment bulb like a taillight can not be flipped that easily. The simpilist solution is to get a + earth bulb.
http://www.dynamoregulatorconversions.c ... s-shop.php

Pete


Easy or not. You MUST figure out how to isolate the socket from the frame so that the socket can be wired with negative polarity. If you can't or don't want to figure this out, forget it and find another solution.

Russ
 
rvich said:
Deets55 said:
rvich said:
If the tail light housing (or the light socket) is electrically isolated from the frame (fender) then you can run wires to it for either polarity. Cuz the electrons nor the LED care what they use as a conductor so long as it makes a circuit. The polarity of the LED matters, not the circuit.

Russ

A double filiment bulb like a taillight can not be flipped that easily. The simpilist solution is to get a + earth bulb.
http://www.dynamoregulatorconversions.c ... s-shop.php

Pete


Easy or not. You MUST figure out how to isolate the socket from the frame so that the socket can be wired with negative polarity. If you can't or don't want to figure this out, forget it and find another solution.

Russ

I agree with you. You must isolate the socket, but in the case of a taillight you must then figure out how to get (+) 12 volt to each of the pins on the back of the bulb an then ( -) Earth to the socket. The LED is looking for that. That all requires a lot of wire flipping to the running light circuit and the brake light circuit. What you are suggesting is quite "do-able", it just comes down to how much work one wants to put into it. Buying the proper bulb and then just plugging it in, on the surface, just seems to be the (IMHO) the best solution.
Pete
 
Yes, I agree too. Unless someone wants to wire the entire bike negative ground it actually makes more sense to get rid of the indexed socket and build your own LED tail light set up with independent lights for tail and stop. Whether or not it will then be DOT approved is beyond the scope of this idea.

Russ
 
Won't work, not with the brake light anyway, will require rewiring of the brake switching circuit. The problem is not in the running light, but with the brake light circuit, as this is switched using the opposite circuit. I ran into this with my seat unit that has an integrated LED, I had to create a new circuit for both the front and rear brake switches using the negative side, wasn't THAT big of a deal, but a deal nonetheless

Anyway, from memory this is a diagram of the circuit I had to make up that's independent of the main harness:

Positive Ground with Negative Ground Lights (2017)
Hi, can you explain how you did this in more detail? I'm trying to get my led lights to work on my commando. The rear light works but the brake light doesn't work
 
Hi, can you explain how you did this in more detail? I'm trying to get my led lights to work on my commando. The rear light works but the brake light doesn't work
Here's the diagram I posted originally

Positive Ground with Negative Ground Lights (2017)
 
The tail light and brake light share a ground. If you are wired normally (+ ground) the tail light circuit feeds -12 volts to the tail light and the brake light circuit feeds -12 volts to the brake light.

Normal + ground
-12 ----- tail -----\
................................. Ground (+)
-12 ----- brake --/

To make it work with a - ground but still in + ground bike
Ground (+) ----- tail -----\
.............................................. -12
Ground (+) ----- brake --/

So, you must electrically isolate the tail/brake light from the rest of the bike or smoke will occur. Then to get the brake to work, it must feed ground, not -12 to the brake light and it will get it's -12 form the tail light. I suspect that both the tail and brake lights are on now.

The correct way to do this is to switch to negative ground - If you use a voltage regulator rather than the bridge rectifier and Zener, its a simple change.
 
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For me it was swapping the two wires from the rec/reg and two wires at the Boyer. That was it. Plus a giant NEGATIVE GROUND sticker near the battery. :p
And of course, the two at the battery :) Red becomes - and Brown/Blue becomes +.
 
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