Fuse size

[hojo in sc]

My friend added driving lights to his Harley, they were "OEM driving lights" and the instructions said to tap into the low beam headlight. After a couple of weeks his fuse blew (10 A). Unfortunately, he doens't know how many watts his lowbeam light is, nor the driving lights.

I am wondering if the instructions should have called for a bigger fuse, wire the driving lights via a relay and seperate fuse, or he was just plain unlucky by having the fuse blow...bike is only about two months old.

tnx

[racer1735]

I'm sure someone will clarify this, but I believe the standard practice is to wire your auxilliary lights to a separate relay. The lights usually have their own fuse, too. You tap into the low beam circuit to draw power in lieu of an on-off switch. You need another circuit to provide the actual 'power' to drive the lights

[Blrfl]

If your buddy's lights are just regular filament lamps, measure the resistance across the terminals of one bulb. Divide 12 by the number of ohms you measured and you'll got the number of amps it draws. (Multiply the amps by 12 and you'll get watts.)

If there's a 10A fuse in the bike, it's there to keep the wiring from melting. Don't replace it with a bigger one.

I'll second racer1735's recommendation of a separate circuit with a relay in it to run the lights.

--Mark

[hojo in sc]

measure the resistance across the terminals of one bulb. Divide 12 by the number of ohms you measured and you'll got the number of amps it draws. (Multiply the amps by 12 and you'll get watts.)
--Mark

Thanks for the tip, if I can convince him to pull the lense off, I will do just that. More than any thing else, I'm very curious about it, as I too am extremely surprised that the instructions didn't call for (and include) a relay. I think the ST has more bulb(s) and with the fuse being only 10 A, I just can't imagine adding a set of lights to that fuse!

[Jim Davis]

Tell him to check the owners manual to see what size of fuse should be in there. Do not go above that size.

I think Harleys add lights on each side of the headlight and usually they do just run off the headlight wire. Not a good thing, but I think many have done it and gotten away with it.

If he has any of the lights of a higher than stock wattage, that could explain the fuse blowing.

The right way to do Aux. Lights is certainly with a separate fused circuit and a relay.