Motorcycle wiring isn’t always a simple thing to figure out. When you’re working on your bike, it’s important to follow some basic fundamentals. See more in the video below:


Understanding how your motorcycle’s tail lights are wired is important for a couple of reasons. First, if you want to add an auxiliary brake or running light, you’ll want to know where to hook it up. Second, for many accessories like the DENALI 2.0 LED lights, you’ll need a switched source of battery power to control the main relay; usually, the brake-light circuit is one of the easiest to find and most reliable sources


  • Check the Wires



Start by gaining access to the lighting wires in the rear end of your bike. You may need to partially disassemble the rear cowling of your bike to find the wires, but usually you just need to remove the passenger seat and have a peek inside.

Here’s a good example to follow. This is the tail light wire plug (three wires) and the license-plate light (two wires) By comparing to the turn signal wires, we know the black with yellow stripe is ground. Because the red wire is found in both circuits, it must be the power. Blue must be, by the process of elimination, the brake light.

Once you can see the wires coming from the lamp housings, take a moment to write them down.
Carefully note whether wires are striped with two colors (white with a black stripe is different from black with a white stripe).

Left turn signal:
wire 1:
wire 2:

Right turn signal:
wire 1:
wire 2:

License plate light:
wire 1:
wire 2:

Brake/tail light:
wire 1:
wire 2:
wire 3*:

*Your brake/tail light is CAN-BUS if it only has two wires. In such bikes, the tail light and brake light signals are contained within a single wire. If the product you are trying to install does not have special instructions for CAN-BUS bikes, please Contact Us for assistance.


    1. Determine Ground


One of the wires attached to each lamp is the ground or negative wire. The ground wire is the same color for every lamp. Look at the list above. The color that is attached to every lamp is ground. Write “ground” next to the appropriate wire color above. The ground color will vary by manufacturer, and could be black, black with a yellow stripe, orange, or green. Regardless, it will be the only wire “common” to all lamps.


    1. Determine Tail Light Positive


The license plate positive wire is the one that’s not ground. This wire will almost certainly be the same color as your tail light positive wire. Write “tail” next to the appropriate wire color above.


    1. Determine Brake Light and Turn Signal Positive


You’ve already determined ground and tail wire colors in your 3-wire brake/tail light. The one remaining wire color is your brake light positive wire. Likewise, the one color other than ground in each of your turn signals is the positive turn signal wire.


    1. Determine Turn Signal Left and Right Positive


This is a little more difficult. But if you can see the wire harness coming from the individual turnsignals, you can determine which is right and which is left. The ground wire color will be the same as for the rest. Watch out for the fact that some motorcycles don’t distinguish left and right colors in the short harness from the tail section to the light itself; that is, it changes color once into the main harness. Always trace back to the main harness to be sure.

A simpler way is “poke and test.” Once you know the positive wires for each turnsignal, fit the PosiTap, hook up your device and test. You have a 50/50 chance of getting it right the first time.

Try this out while looking at the bike. It’s a lot easier to do this with it in front of you than to try to remember.

13 thoughts on “How To Determine Which Wires Are Your Motorcycle’s Brake Light Tail Light And Turn Signal Wires

  1. How to find Wich wire on your swich Harley Davidson 1975

    1. Your best bet will be to use a multi-meter to detect which wire is receiving a 12V signal when your headlight switch is activated.

  2. How does the taillight wire harness unplug from the taillight on. A 2001 indian spirt

  3. Why is my 1990 Suzuki intruder 750 head light very dim and the blinker lights come on but go to use them they don’t work when I flip to the left the front left goes out but back left goes brighter I do it to the right they get brighter but also don’t blink and again my head light barley even has a glow I need help I’m to the point where I wanna sell it cuz I’m so mad but I love the bike and it’s my first ever owned!! Please help me

  4. hey Marc my bikes tail light is not coming on at all, do you have any idea what the problem could be?

  5. ? How to wire up turn signals on a 1982 Yamaha 920

  6. I am trying to fit an extra brake light to my Honda cb500, there are three wires in the harness on the bike green earth, green yellow stripe brake light switch , & a brown wire ,the extra light I want to connect has only two wires ,black negative & red positive, I have connected the black to green earth wire & red to green yellow brake light switch wire but no luck so should I connect the red wire to the brown wire ? can anyone help ?

  7. Hi – I’ve tried everything to install an aftemarket integrated LED
    tail light on my 2000 ZX-7R 750P. The LED light has a 3 wire harness connected that fits perfectly into the bike’s harness. It also contains 1 yellow and 1 blue wire which I have spliced into the positive left and right wires coming from the bike’s harness. Rear brake light doesn’t come on when activated, front brake activates light intermittently. I’m confident the switches aren’t bad. Turn signals r all screwed up too. I’m about to throw the thing into the woods.

    Thanks – Steve

    1. I have the exact same bike & the exact same problem. It’s driving me insane.

  8. I have a 2007 BMW F650GS. I am trying to connect a Bluetooth unit onto the signal and brake lights for a rig for my helmet. I am looking at the loom under the seat where a previous owner connected wiring for a sidecar’s lights. Is there anywhere that one can get a wiring diagram with the color coding on it to make it easier on myself?

  9. I have a light blue ,orange, a white and green with yellow stripe to Browns the rest are green wires. When I match the colors together everything’s all jacked up how do I fix this

    1. What’s your bike, Tony?

      1. It looks like you might have a Honda, because their ground (negative) is typically green like the grass which is on the ground.

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