Added a tail/brake light

I went to Wal-Mart and picked up a small red LED 12V marker light from the trailer/automotive section. It's about 2-1/4" wide by 3/4" tall x 1" thick. Inside the epoxy sealed lens is two super bright LEDs mounted on a PCB with a few resistors and a diode. The light has two mounting holes about 1-15/16" apart.
I mounted this light on the lower back horizontal tube of the luggage rack (of which I have yet to tote any luggage in). I drilled four holes; two for the mounting holes, one between these two for the wires to enter the tube, and one all the way around on the left side bottom of this same tube, next to where it butts up against the main vertical roll bar tube. I ran the wiring from the middle light hole, snaked it out of the exit hole near the roll bar tube, and grommetted both holes with appropriate sized grommets. Then I drilled the two mounting holes on the lens bigger to accept two of my smallest rubber grommets. This will provide some amount of crack protection and shock mounting for the lamp. I then mounted the lamp with two stainless steel sheet metal screws. I'll probably go back and goop copious amounts of black RTV around the mounting and wiring holes to help prevent rust and water getting inside the tubing.
Since I wanted to have both a tail and a brake light, I figured a good way to make the single-element light do double-element duty. First, I traced out the wiring for the brake safety switch and bypassed this by cutting and crimping the green/yellow and brown wires going to this switch together. I did the splice up where the brake safety switch harness enters the main harness junction, which is very close to where my wires come out of the luggage rack tubing. Now I can start the cart without depressing the brake, which for me is not an issue. I've always thought it is kinda funny that YD put in this "safety feature" but left out a friggin' parking brake! :blink:
I decided to use the lighting circuit to power my lamp. I cut the black and red wires leading to the headlights about an inch from where they come out of the main harness. I spliced all the black wires and my negative lead to the new taillight together. Then I spliced the red wire leading to the headlights together with the red wire the engine, and along with these two, I spliced one of the wires from the brake switch (doesn't matter which) and one leg of a 1K 1/4 watt resistor together (you can pick up the resistor at Radio Shack if you don't have one handy). The other leg of the resistor is spliced together with both the positive lead of the new taillight and the other wire from the switch.
If this sounds confusing, it is (probably because I don't know how to 'splain it any less verbose!). So, the long story short is that we're feeding the new taillight throught the 1K resistor when the brake is off. This makes it illuminate dimly. Then we are bypassing the 1K resistor with the brake switch when the brake is applied. This puts full lighting ciecuit voltage to the taillight, making it illuminate at full intensity.
I futzed around with my resistor decade box trying different resistances, and 1K seemed to be a good value to make the difference between marker light mode and stop light mode very noticeable, while keeping adequate marker light illumination. I would say it's about twice as bright with the brake on, yet still easily seen (at least at night) when the brake is off.
Here's a quick schematic...

Here's a picture of the light as seen from behind...

Attached Image

Here you can see where I put the grommets for the wiring and vibration resistance...

Attached Image

Here's where I ran the wiring out of the tube. I made all my splices down where the large vertical roll bar is bolted to the frame.

Attached Image

I should also note that it really doesn't matter which way around one installs this lamp, since we're feeding it AC from the lighting coil. I only referred to the + and - leads for convenience. If you're not sure which is which, it doesn't matter ;)

It should matter, LEDs are designed for one polarity. If you cross the wires the LEDs will blow. I dunno if the marker light has a diode in it to prevent damage if the polarity is reversed though. It should not be a/c current in the wires. The electrical to charge the battery has to be D/C. The only A/C in the circuit should be in the alternator before the diodes. The D/C after the alternater can be a pulsating D/C, which is normal. You can find the amount of pulse, or voltage ripple, in the system by putting a voltmeter on A/C and taking a reading.
I think that is all I have to say.

It should matter, LEDs are designed for one polarity. If you cross the wires the LEDs will blow. I dunno if the marker light has a diode in it to prevent damage if the polarity is reversed though. It should not be a/c current in the wires. The electrical to charge the battery has to be D/C. The only A/C in the circuit should be in the alternator before its diodes. The D/C after the alternater can be a pulsating D/C, which is normal. You can find the amount of pulse, or voltage ripple, in the system by putting a voltmeter on A/C and taking a reading.
I think that is all I have to say.

It should matter, LEDs are designed for one polarity. If you cross the wires the LEDs will blow. I dunno if the marker light has a diode in it to prevent damage if the polarity is reversed though. It should not be a/c current in the wires. The electrical to charge the battery has to be D/C. The only A/C in the circuit should be in the alternator before its diodes. The D/C after the alternater can be a pulsating D/C, which is normal. You can find the amount of pulse, or voltage ripple, in the system by putting a voltmeter on A/C and taking a reading.
I think that is all I have to say.

boy im a retard with these post copies :blink:

Hehe - "I think that is all I have to say" and you said it three times :D :lol:

Ok...

1) The lighting circuit on our carts are separate from the battery. It supplies a non-rectified AC voltage to the lamps. Look at the circuit diagram for the cart - there are no rectifiers in the light circuit.

2) The LED only emits light when it is forward biased. Diodes only flow current when they are forward biased. When they are reverse biased, up to it's peak inverse voltage (breakdown voltage) it will conduct very little. The thing about LEDs is that their PIV is usually low, around 5 volts or so. So in this case, yes a simple LED with a current limiting resistor in series cannot be directly operated from an AC source, at least one that has a higher peak voltage than the PIV of the LED.

3) This lamp has an internal 1N4004 rectifier that allows it to operate at 12VAC, so one can operate it from our lighting circuit without any problems. I guess I should have made it clear in my post that this is what the diode in the lens is for. :D

is it possible to run the wires strieght to the battery for just a tail light. i don't really want to mess with the electrical system :D

Thanks,
-STEVE-
Yerf-Dog 3209

Wow! :o Id look into this more if I had my voltmeter, too bad it got stolen with the rest of my tools down in mexico.

Yeah, you'll need a switch though, unless you're just using it as a brake light.
It's really not too hard at all to do it to the lighting circuit though, I would urge you to try.

Doggone banditos!
:angry:

If I wanted to have just a brake light for when I am breaking would this work?

-I run a positive wire from the positive in my battery to the poitive on my 12v led light. Then I ran a wire from the negitive of my light to one end of the brake safty switch. Then I ran the last wire from the other end of my brake safty switch to the neggitive on the battery. :blink:

That would work fine. All you'd have to do is follow my schematic, but leave out the resistor. This is what I originally did, but I looked at how easy it would be to modify the circuit for a running light by just the addition of the 2 cent resistor.