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Hey everyone! Was looking for some guidance. I'm upgrading my headlight to LED to lessen the pull on the battery for my 79 kz750 and was wondering if someone could tell me which prongs on the stock headlight are the ground, high, and low beams. Thank you kindly in advance.

I don't have a 1979 KZ750-B3 wiring diagram, but on the KZ wiring diagrams I've seen, Red-Yellow is the low beam, Red-Black is the high beam & Black-Yellow is the ground wire. You should be able to trace the wires at the connector to see which prong is which.

I have a general question about this topic. I hope it is not considered a hijack..........

I don't know much about electricity, so I hope one of the resident experts can enlighten me.

As I understand, an LED bulb requires only a fraction of the electrical power neede to get a similar level of lighting from an incandescent bulb. Since the motorcycle's electrical system is designed for the higher usage bulb, it will send that amount any time the circuit is activated.
Since the LED requires so much less, a step-down device of some sort is needed to prevent an overload at the bulb. Said device in some way dissipates the excess, thus wasting a good bit of energy and not saving the system at all.

Put a simpler way, where does the excess electrical power go?

Am I off in the weeds here?

TexasKZ wrote: I have a general question about this topic. I hope it is not considered a hijack..........

I don't know much about electricity, so I hope one of the resident experts can enlighten me.

As I understand, an LED bulb requires only a fraction of the electrical power neede to get a similar level of lighting from an incandescent bulb. Since the motorcycle's electrical system is designed for the higher usage bulb, it will send that amount any time the circuit is activated.
Since the LED requires so much less, a step-down device of some sort is needed to prevent an overload at the bulb. Said device in some way dissipates the excess, thus wasting a good bit of energy and not saving the system at all.

Put a simpler way, where does the excess electrical power go?

Am I off in the weeds here?

The bulb will only pull the power it needs. No step down or what have you needed. Of course this assumes the LED is 12 V and not something lower.

Regarding the bikes charging system in general, since the generator is 3 phase permanent magnet (which I think the bike in question is), then the amount of power generated is more or less constant depending on rpm and saturation rate (at some point as the rpm's rise the power output maxes out). The bike consumes the amount of power it needs and then there is excess which must be discarded some how. With a typical shunting type R/R the excess power is shunted back to the stator where it creates heat and shortens stator life. That's why I keep harping on the use of SERIES type R/R's; they don't shunt the current back thus they protect the stator. And adding things like an LED headlamp, which seems good in theory, can be bad for your stator unless it's weak already.

No eBay APP ID and/or Cert ID defined in Kunena configurationNo eBay APP ID and/or Cert ID defined in Kunena configurationThe LED H4-type motorcycle headlights I've seen have some sort of device that uses around 40W or so & have an aluminum heat sink to dissipate the heat. I don't know how they work, but I have assumed one purpose of the device is to have some way to deal with the excess voltage, converting it to heat. EB search >>> Led motorcycle headlight H4

Because most electrical systems are voltage-based, meaning that it is the voltage that is regulated, any device rated for that voltage will only use whatever current it needs.

A raw LED only uses about 2 to 3 volts, so12v would normally blow it up. To get around that, a simple resistor can be used to reduce the voltage. Another method is to put more of them in series. If one of them needs 2v, six of them in series would use 12v.

But LEDs are extremely sensitive to over-voltage, so normally, they use a combination of multiple LEDs in series plus a resistor. The resistor acts as a ballast. By burning away some power as heat, it can help regulate the voltage to the LED stack. That is, when the bike voltage goes from 12 to 14 volts, the extra current through the resistor increases the voltage drop on the resistor. This way the led stack only sees a slight voltage increase, instead of the full 2v increase.

Nowadays, with really high power leds, you're more likely to see an actual regulator for the led stack.

Got the headlight installed. It plugged right in with no issues. We shall see if I habe any adverse affects over time.

Another thing worth checking is the general health of your wiring. These bikes are getting 40+ years old now, and since the headlight has no relays, any corrosion or wear in any of the multiple plugs and switches will reduce the voltage (and therefore output) of your headlight.

It's not unusual to see a couple of volts dropped on the headlight. A bulb at 14V will put out over a 3rd more light than the same bulb at 12V, so giving your switches and plugs a good clean can make a big difference. This applies to old and new headlights.

loudhvx wrote: Because most electrical systems are voltage-based, meaning that it is the voltage that is regulated, any device rated for that voltage will only use whatever current it needs.

A raw LED only uses about 2 to 3 volts, so12v would normally blow it up. To get around that, a simple resistor can be used to reduce the voltage. Another method is to put more of them in series. If one of them needs 2v, six of them in series would use 12v.

But LEDs are extremely sensitive to over-voltage, so normally, they use a combination of multiple LEDs in series plus a resistor. The resistor acts as a ballast. By burning away some power as heat, it can help regulate the voltage to the LED stack. That is, when the bike voltage goes from 12 to 14 volts, the extra current through the resistor increases the voltage drop on the resistor. This way the led stack only sees a slight voltage increase, instead of the full 2v increase.

Nowadays, with really high power leds, you're more likely to see an actual regulator for the led stack.

Well then, does the LED headlight actually reduce the load on the electrical system? The heat sinks on the examples above suggest to me that the load to the bulb is essentially the same, and whatever the LEDs don't need gets wasted as heat. Is that correct?

Always good advice with an old electrical system.

Irish Yobbo wrote: Another thing worth checking is the general health of your wiring. These bikes are getting 40+ years old now, and since the headlight has no relays, any corrosion or wear in any of the multiple plugs and switches will reduce the voltage (and therefore output) of your headlight.

It's not unusual to see a couple of volts dropped on the headlight. A bulb at 14V will put out over a 3rd more light than the same bulb at 12V, so giving your switches and plugs a good clean can make a big difference. This applies to old and new headlights.

Lkean2135, attached is a wire diagram for the 79 KZ750 Twin for your ref.

TexasKZ wrote:

loudhvx wrote: Because most electrical systems are voltage-based, meaning that it is the voltage that is regulated, any device rated for that voltage will only use whatever current it needs.

A raw LED only uses about 2 to 3 volts, so12v would normally blow it up. To get around that, a simple resistor can be used to reduce the voltage. Another method is to put more of them in series. If one of them needs 2v, six of them in series would use 12v.

But LEDs are extremely sensitive to over-voltage, so normally, they use a combination of multiple LEDs in series plus a resistor. The resistor acts as a ballast. By burning away some power as heat, it can help regulate the voltage to the LED stack. That is, when the bike voltage goes from 12 to 14 volts, the extra current through the resistor increases the voltage drop on the resistor. This way the led stack only sees a slight voltage increase, instead of the full 2v increase.

Nowadays, with really high power leds, you're more likely to see an actual regulator for the led stack.

Well then, does the LED headlight actually reduce the load on the electrical system? The heat sinks on the examples above suggest to me that the load to the bulb is essentially the same, and whatever the LEDs don't need gets wasted as heat. Is that correct?

That depends. Is a 60w LED headlight designed to dissipate 60 watts, or is it designed to produce the equivalent amount of light as a 60w conventional bulb.?

Obviously, if an LED bulb is designed to use 60w, then you won't save any electrical power versus a regular 60w bulb. But there might be a lot more light.

If the LED puts out an equivalent amount of light as a 60w bulb, then the LEDs might use a lot less power to do that, so then you would save electrical power. This is the case with home lighting, and I would assume it may be the same with automotive lighting, but I don't know for sure.

The regulator for an LED would not be like a shunting voltage-regulator. A shunt voltage regulator has to get rid of power because the alternator output is too high. The regulator for the LED bulb would be a series-pass, meaning it regulates the voltage to the bulb by only letting through however much current the bulb needs while monitoring the voltage on the bulb. There are some ways of regulating this that are far more efficient than other ways. Regulating power will always dissipate some amount of heat as wasted power, but a modern, high-frequency switching regulator is more efficient than a passive resistor or even an active transistor. But it costs more in terms of control circuitry, so sometimes a passive resistor is much cheaper even though it wastes a bit more power.

The heatsink may be necessary for the regulator, or it could be to cool the LEDs somehow, and it does indicate some wasted power, but a halogen bulb also gets very hot, and that is energy wasted as heat instead of used as light.