Watts are a component of Ohm's Law. If you know volt and watt you know amps, and wiring is rated to carry X number of amps. The wattage will vary based on volts and amps, all three are interdependent, but to figure the load a wire can handle you must find amps.

 

google "Ohms Law"

Watts is an expression of the amount of voltage in a circuit times the amount of amperes ( or current draw) a device uses.

Once a designer knows the resistance in the circuit, and the voltage they can figure out what size and type of wire, as well as the type of insulation based on a whole bunch of things, environmental being a lot of it. Then there are the connectors the bulb uses to connect to the harness. Is there enough surface area for the current to pass and not overheat and melt?

So wires are chosen for current draw, voltage ( dielectric strength of the insulation factors here too) , loss in the length of the wire over distance ( line loss due to the resistance of the wire) etc etc etc.. Same thing with connectors and fuses.

If a circuit is designed for 5 amps, 12 volts, at say 18 gauge stranded wire, and it is an inductive circuit such as an incandecent light, you might find a 7.5 amp fuse in it, possibly 10, assuming it is not powering other lights on the same circuits.

Lets assume you have a house, and the breaker box has 15 amp breakers, and the circuit is wired with 14 guage wire. You have a toaster plugged into it and all works well.

One day you get a new coffee maker and a waffle iron. You go to make breakfast and turn all of them on only to find the amount of total wattage of the devices added up, divided by 120, exceeds the number 15, which is the amount of amperes the circuit is designed to carry safely but the breaker trips, but you want to make coffee, toast your english muffin, and make belgian waffles all at once, so you decide for whatever reason you can slide a 30 amp breaker in the panel and make breakfast without interruption.

That works well for the first few minutes until the smoke detectors start chirping because the undersized wire behind the drywall and the undersized outlet in the wall (yes even the outlets are rated for capacity) have started a nice little fire because they have overheated because you are drawing more current ( and by ohms law watts) than the circuit is designed for, and you suddenly realize lunch is going to be had someplace besides home for a while.

Bike wiring is the same way. Start tapping into wires to power added devices, add devices that draw more current than the wire and connectors are rated for, and you can end up with things burning, melting, or otherwise not working as you would like them to.

(Next we can discuss the ratings of contacts in the switches and relays and the finer points of arcing and erosion).

 

I've had my PIAA's for 5 years now with no problems. They come in different "colors". I also have them in the driving lights.

 

Yep big time difference.

 

To the OP, Yes the 100 watt ones will melt your plug, Don't ask me how I know except I can tell you that someone out there owns a sporster with a new plug installed in the bucket. Silverstars help but they don't last long. The PiAA extreme white is really white but are around 50 bucks. I saw a Trucklite LED the other day on a bike and they are $260.00 but are basicallyliftime bulbs lasting 50x what a normal bulb does. Thing was a day lighter and hardly drew any power. Thats what I am saving my pennies for. Brightest daylight looking light I have ever seen. I was amazed.

 

Any bulb that is D.O.T compliant is no brighter than any other D.O.T bulb.The more tint it has the less light it emits.The cheapest upgrade would be the 65/70 osram bulb wired with 12 ga wire and a good relay.

www.easternbeaver.com sells relays and prewired kits

 

you can find bakelite headlight connectors at napa auto parts. i hate the stock harley headlight plugs so i soldered the better bakelite three prong plug in where the nylon plastic connector was. i am also using the E-code headlight, made for overseas, france and germany and it is a huge improvement. you can get hella or cibie and they're glass rather than the chromed plastic reflector that harley uses stock. with the same bulb i had in the stock headlight housing i now light up the road where i want to see rather than splattering lots of light around to oncoming traffic, the ditch to the right and for illuminating overhead signs. i found out about the e-code headlights and studied them before spending less than 50 bucks for it. they claim that they put out 400% more light, but i doubt it. what they do is focus the beam right down your lane, the side of the highway you're using. if you go this route be sure to get the hella or cibie headlight that's made for germany or france because the brits drive on the wrong side of the road and therefore the beam would be wrong for riding on the right side like we do here in the usa. it's the best bang for the buck by far.

 

You can find the amp draw for the stock bulbs in your owners manual. The stock bulb in my 2009 FLHP is rated at 4.58 - 5.0 amps. I use a PIAA 60/55 4000k bulb. It is PIAA part number 70456.

 

Osram 80/100.

 

Osram 80/100 bright durable and under $20.