Headlight Help Page

Factory Relays and Control Units: Some bikes actually come with built-in relays on the headlight. These can be not so obvious, and can be built into a control unit which monitors the bike's wiring.

The only way you can add a relay kit to a bike like this is to rewire the bike to work normally. That is, so that the built in relays are by-passed, and current is fed to the Relay Kit directly from the HI/LO switch. You may have a warning light come on permanently if you do this.

Check your wiring diagram carefully to determine where the current to your headlight bulb comes from. If it goes through the left side HI/LO switch and then to the headlight bulb, you can be sure that your bike does not have relays. If the HI/LO switch wires lead to a control box, it likely has relays built-in.

If you have factory relays on your bike, YOU MUST ONLY USE A STOCK WATTAGE HEADLIGHT BULB. A high watt bulb could cause a serious problem using stock relays and wiring.

Headlight Examples

Below: Some bikes have an extra headlight protector built into the fairing which prevents cooling air from the actual headlight lens. Looks good, but makes a bike like this not a good candidate for a high wattage bulb. Many older bikes though, do have a rather large headlight and likely heat will not be a problem. Keep in mind that many RT or RS bikes are not built for city driving. If you spend a great deal of time in traffic or a city, a high watt bulb might not be a good idea on a bike like this.

BMW

This style headlight can get hot! If the lens is not directly hit with cooling air, then it is not a good candidate for a higher wattage bulb. Some bikes have built in headlight shields, some have added shields to their headlights. Both types prevent good cooling of the lens and housing.

Many older Japanese bike fairings are quite open on the back, which helps airflow.

Headlight Cooling Notes:

- headlight covers reduce cooling

- flush to fairing headlight are OK if the headlight lens itself is exposed to the wind.

- standard bikes with no fairing have well cooled headlights

- the larger the headlight shell, the cooler it stays

- fairing headlights can be tightly fit to the fairing, if rubber strips are present to seal it, these can be removed for better cooling

- newer headlight housings use lighter plastic materials that can melt

- newer fairing designs wrap around and have an inner liner and don't cool well

- older fairing designs are open on the back which helps cool the bulb

HI and LO Beam ON Together

I now make and sell a special Heavy Duty H4 Kit for bikes like this, to allow a higher wattage bulb to be used. However, the biggest problem for these bikes is the high heat buildup, even with the stock bulb at times. If you are using Auxiliary Lights too, then it is a good idea to change your bike over to separate HI and LO beam headlight. Below is a photo of where the jumper is to disconnect this system on a BMW K75.

Remember that your bike does not have an unlimited supply of electricity and with both beams on your bike might already be close to it's maximum wattage. If you add auxiliary lights or heated clothing, you might find your battery drained, leaving you stranded.

Add up all your wattage on the bike and subtract from your bike's alternator output and you will find out your excess power that is available. If you have a voltmeter on your bike, then you will know when your running voltage drops below ~12.8 Volts that you are draining your battery and must turn off something in order to keep your bike's battery charged.

Calculating Excess Electrical Capacity

The Powerlet website has an excellent article here.l

BMW K75 - jumper to unplug, so that low beam doesn't stay on with high beam.