LED stop/tail light

[Mosin]

I have just bought an LED stop/tail lamp similar to this one and I have got myself totally confused with how to wire it in. My bike is running a 12 system with a positive earth. I have tested the lamp across a battery on the bench and all seems to work fine. The black wire goes to the negative side of the battery, and the red and blue go to tail and brake respectively. All good so far 

Now... If the bike had a negative earth, then this would be a piece of cake, but it doesn't.    My initial thought was that I would simply wire it the other way around, with black going to positive (earth) and the other two wires going to negative via their separate switches. But this didn't work at all. Now my brain is knotted up like so much spaghetti and I can't fathom it out at all. Please can someone assist?

[Triton Thrasher]

The simple answer is you have the wrong LED.

[Mosin]

Bugger. I had a horrible feeling that someone was going to say that. Pity the vendor didn't think to mention in the advert that there were different types depending on the polarity of the bike. 

[berger]

triton thrasher is right , I was given some LED's to fit on the front for day time riding and had same problem so now they hang over the lathe lit off an old battery

[Triton Thrasher]

The seller may not know that any vehicles were +ve earth.

[Greybeard]

This may be a dumb question, but if the LED itself is not using the bikes earth as a return why can't the wires feeding it just be reversed?

[morris]

This may be a dumb question, but if the LED itself is not using the bikes earth as a return why can't the wires feeding it just be reversed?

LED’s work in only one direction. As there is only one return (- in this case) and two (+) feed wires (stop and tail) you cannot simply switch them. If you want to make it work on a + earth system you would need to connect both feed wires to (+) earth and you would only have one wire left to connect to the brake switch and tail light feed.

[Bsareg]

Morris is spot on. Easiest way if still using a mechanical regulator would be to reverse battery leads and flash dynamo to change bike to - earth.

[Triton Thrasher]

Morris is spot on. Easiest way if still using a mechanical regulator would be to reverse battery leads and flash dynamo to change bike to - earth.

And don’t forget you’ve done it!

[RogerSB]

Here's my own customised + earth 1960 A10 GF wiring diagram with LED stop/tail and pilot light. Not all the wire colours are as they were originally.

[Greybeard]

This may be a dumb question, but if the LED itself is not using the bikes earth as a return why can't the wires feeding it just be reversed?

LED’s work in only one direction. As there is only one return (- in this case) and two (+) feed wires (stop and tail) you cannot simply switch them. If you want to make it work on a + earth system you would need to connect both feed wires to (+) earth and you would only have one wire left to connect to the brake switch and tail light feed.

Ah, yes, I can see that. However, with a simple two-wire LED should be possible to reverse its feed.

[duTch]

 

Morris is spot on. Easiest way if still using a mechanical regulator would be to reverse battery leads and flash dynamo to change bike to - earth. 

 Exactly what I did, but for other reasons as well....

[bsa-bill]

Morris is spot on. Easiest way if still using a mechanical regulator would be to reverse battery leads and flash dynamo to change bike to - ea

Yep - Did this on my A10, easy to do and yes if you have or can borrow a label printer stick labels on frames tubes (side and across) "negative earth", or just buy and use sticky labels

[BSA_54A10]

This may be a dumb question, but if the LED itself is not using the bikes earth as a return why can't the wires feeding it just be reversed?

Because the bike grounds + sp all of the body parts are + so the base of the globe will be + .
However it needs to be -
Now if the entire tail lamp can be insulated from the bikes frame then it can be wired with a - wire to the globe base and then an electrically isolated switch to send + to either one of the pins.
For a stop only that is a piece of cake, you just run a wire + battery through the switch but the tail lamp is the problem unless he fits yet another switch battery + to tailalmp switch to tail lamp.

The nay time the light fitting touches the frame the fuse will blow.

Lot easier to get the correct globe or swap the bike to - earth.