Help please New undertail Led problem

[saul]

OK guys this is the thing.

I have installed my under tail and it looks pretty good, but I have a small issue that needs to be sorted.

My new LED rear lights do not appear to have a break light capability i.e Turn the park lights on, rear light works: niceone: Put the main lights on, rear lights work Put foot on the rear break or pull the front break and no extra light comes on.

I don't know much about wiring but all appears to be solid and correct.

As a test I took one of the LED bulbs out and put the original bulb in and that actually worked with the brake and lights.

So does that mean that the LED is a light only type bulb (no brake light capability) or does it mean that I am missing something?

I am leaning to I have missed something but you never know

Thanks guys appreciate your time

[**R1**]

Do you have a pic of the wires? I helped a mate do one a while ago and it all workd sweet, where did you get the undertail?

[WildBoarMouse]

If it's an array of LEDs, you'll probably need a current limiting resistor to limit the brightness/current when used as a tail/park light (i.e. not braking). I'd expect to see the LEDs most likely wired straight to 12V through the brake light wire, but would also expect to see a resistor in-line with the park-light wire. From your previous light you should have three wires. Ground, brake, and park. Check the wiring instructions again and see if you need a resistor (probably a low ohm, high wattage one) between brake and the LED tail light.

If you post all the specs on the current draw, forward voltage blah blah on here, someone will be able to work out a resistor value fairly quickly. Idealy a link to the specs would be better than listing them all... in case something useful gets left out (i.e. luminesence vs current draw)

Hope that's of some small help

[saul]

Do you have a pic of the wires? I helped a mate do one a while ago and it all workd sweet, where did you get the undertail?

Hi R1

Grabbed it of ebay ages ago Pimpbikes.com.

Looks nice and a lot better than all the crap that used to be there.

[saul]

If it's---small help

There were no instructions, but that sounds like it could be the answer.

I have a resistor type box I was going to use for the indicators to stop the fast flash problem. I didn't think that the stop lights would be an issue.

Do you know what the wiring colours for Ground, brake, and park are.

Thanks for the help

[WildBoarMouse]

Hi, I've no idea what the wire colours would be. You'll want a multi-meter to help solve that. Shouldn't take more than a minute or two.

To work out the resistor (roughly): measure the current sourced by the new tail light when connected to 12 V. measure the *actual* voltage across the terminals. Multiply the current by 0.6 (guesstimate) and divide the measured voltage by this value.

This gives you a resistor value in Ohms. Remember that when measuring the current you're probably dealing in milli-amps so take note of the decimal point.

To work out the wattage of the resistor: multiply the measured current by 0.4 (1 - 0.6) and multiply it by the measured voltage. This will give you the power that the resistor will need to disapate (in heat) in Watts.

example:
Measured V: 13.6 V
Measured I: 400 mA (0.4 A)

Resistor: V / (I * 0.6) = 13.6 / (0.4 * 0.6) = 56 Ohm (approx)
Wattage: V * (I * 0.4) = 13.6 * (0.4 * 0.4) = 2.2 W (approx)

So, you'd probably want something like a 2-5 W, 50-60 Ohm resistor - or there abouts

Anyway... that should give you a *rough* idea of how to work out a value. Just remember that just because you're limited the current to two thirds of the original current, this does not mean that the brightness will be two thirds. You don't have any of the specs here so you'll have to guesstimate. If you want a play, alter the resistor between 50 and 100 Ohm (in this example) and play around with the brightness until you're happy with it.

Someone can check my theory/calcs if they like

[saul]

Hi, I've no idea---
Someone can check my theory/calcs if they like

Shite you clever basta-d

[**R1**]

Hi R1

Grabbed it of ebay ages ago Pimpbikes.com.

Looks nice and a lot better than all the crap that used to be there.

I just sold one the same on trademe, i ended up buying 2 i kept the hotbodies 1 and sold the other for $200, they look fantastic tho. good luck.

[saul]

I just sold one the same on trademe, i ended up buying 2 i kept the hotbodies 1 and sold the other for $200, they look fantastic tho. good luck.

Oh yeh I saw that on trademe

I do agree with your comment about it, but over all it does look good I colour matched it.

Well mate where are the fitting instructions cause I didn't get any with mine but if you bought yours new you would have.

Those instrctions would have the info for the wiring wouldn't they???

Cheers

[saul]

Any other comments guys ???

Thanks

[**R1**]

Oh yeh I saw that on trademe

I do agree with your comment about it, but over all it does look good I colour matched it.

Well mate where are the fitting instructions cause I didn't get any with mine but if you bought yours new you would have.

Those instrctions would have the info for the wiring wouldn't they???

Cheers

sory dude instructions went with it...ill email the guy i sold it to see if he can help.

[froggyfrenchman]

I would hook the park lights up to same as tail light, then hook brake up to what is currently park. Just my opinion

[notme]

As a test I took one of the LED bulbs out and put the original bulb in and that actually worked with the brake and lights.

My brain is running slow today, i have a cold...so forgive the silly questions - but did you buy LED bulbs that fit into standard bulb holders, or did you get an undertail assembly that has LED light built in and wires coming from them for you to connect.... ?

[kawa10]

So does that mean that the LED is a light only type bulb (no brake light capability) or does it mean that I am missing something?
i would say yes and yes.

[Dafe]

----

I current drop 12VDC to 5VDC alot. For 5VDC LED's, I always use a standard 1/4 watt resistor, Value: 1200 Ohms.
Be Warned: If you are using Superbright 5V Leds, they tend to have a much lower foward voltage, usually around 2-3VDC, you will need to use a 2.2K resistor to drop from the 12VDC.
When experimenting with brightness, be sure to you your heaviest resistance values first to save blowing LEDs, e.g. Start with 2.2Kohms as your 12VDC dropping resistor value before trying smaller values.

I can almost certainly guarantee that if you use the values above, You'll have no LED's left.