Headlight Blows Fuse

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Discussion Starter · #1 · Dec 8, 2008

so I’m coming around a particularly dark corner Saturday. Flick on the high beam (after blowing the horn of course), and WHAM! All dark.

Blew the headlight fuse when I went to the highs. So of course, I replace the fuse and hit the high beam again and WHAM! All dark.

One fuse left – got me back home.

Let the troubleshooting begin – pulled the high beam bulb, hit the high beam – 12 volts at the connector. Put the bulb back in, did the high beam mod (keeps the low beam on even when you hit the high beam) – no problems.

Guess I’ll wait for it to pop again to find the short, unless anyone has some ideas about obvious places to look.

And of course – thanking the forum in advance!

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The horn is on the same fuse I believe. Do you loose your fuel guage too. If there is no short in the headlight wiring you might try looking at the wiring for the horn. In some cases it will rub the horn bracket and short out. Something to think about.

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…Flick on the high beam (after blowing the horn of course), and WHAM! All dark.

Blew the headlight fuse when I went to the highs. So of course, I replace the fuse and hit the high beam again and WHAM! All dark.

One fuse left – got me back home.

Let the troubleshooting begin – pulled the high beam bulb, hit the high beam – 12 volts at the connector. Put the bulb back in, did the high beam mod (keeps the low beam on even when you hit the high beam) – no problems.

Guess I’ll wait for it to pop again to find the short, unless anyone has some ideas about obvious places to look. …

I’m not quite sure what you have going. Did you do the modification to permanently light the low beam before or after you first overloaded the “LIGHTS” fuse?

This 15 A fuse, that feeds the blue wire and powers running lights, license plate lights, and the low and high beam bulbs should not blow with both low and high beam on, although with both HI and LO beams on this circuit is seeing about 13 A.

I’d look for bad insulation on the high beam circuit (White wire from the left hand controls pin #4 to pin#2 of the headlamp connector) or in the “HI/LO” switch itself.

BTW, the horn is not on this circuit, it’s powered by the Orange with White striped wire from the “ACCY” fuse.

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Check your left hand control for a pinched wire.

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It is a wiring problem, bulbs don’t blow fuses, bare wires contacting ground blow fuses.

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Discussion Starter · #6 · Dec 8, 2008

I know it was not the bulb or the horn blowing the fuse.

It is a pinched wire somewhere, but as always, intermittent problems are the hardest to troubleshoot. I’ll pop off the hand control tonight and take a look.

The horn reference was about hitting the wrong button when trying to get the high beams on. kind of like hitting the CAPS LOCK WHEN TRYING TO HIT THE SHIFT KEY.

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I know it was not the bulb or the horn blowing the fuse.

It is a pinched wire somewhere, but as always, intermittent problems are the hardest to troubleshoot. I’ll pop off the hand control tonight and take a look.

The horn reference was about hitting the wrong button when trying to get the high beams on. kind of like hitting the CAPS LOCK WHEN TRYING TO HIT THE SHIFT KEY.

Rather then installing fuses if you have a dvm meter you can set the meter to ohms and pull the bulb and insert the meter in the socket. If you then manipulate the wiring you well see 0 ohms when the wire goes to ground as long as the other end of your meter is contacting ground. It really is the easiest way to start a search for a short.

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Is there a way for you to measure the actual current draw? If the calculated load is 13 amps, and it is on a 15 amp fuse, that really is not enough margin for loads such as incandesent lamps that have a higher in rush current, than operating current.

Of course fuses are also designed to take a greater load for a defined number of milliseconds, (depending on designed characteristics). You may just be on the edge of exceeding the ratings. When the fuse blows, does it look like it just barely melted through, or is the fuse element completely blown away. This can be a clue as to whether you are looking for a short, or just an overload.

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My bad on the fuse. When I had my problem it was the tail light that went when the fuse blew. Sorry.

If you have the fuse box exposed and the ingition one when you jiggle the wires you will get immediate gratification. I was surprised how bright a spark that little fuse created when it blew.

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I need to get my amp meter out. I doubt this circuit pulls that much amperage. It would be 1/4 of the total amperage for the motorcycle……That just doesn’t sound right.

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I need to get my amp meter out. I doubt this circuit pulls that much amperage. It would be 1/4 of the total amperage for the motorcycle……That just doesn’t sound right.

It does seem rather high but that’s with both headlamp bulbs on and assuming a regulated voltage for the light circuit of 14.5 VDC. Most lamp bulbs are rated at 12.8 VDC so the list is:

low beam bulb is 55 W @ 12.8 V, 70.6 W @ 14.5 volts or 4.87 A (manual lists 4.3 A)

high beam bulb is 65.3 W @ 12.8 V, 83.8 W @ 14.5 volts or 5.78 A (manual lists 5.1 A)

rear tail lamp bulb is 8.3 W @ 12.8 V, 10.65 W @ 14.5 volts or 0.73 A (manual lists 0.59 A)

front running lamps are 16.6 W @ 12.8 V, 21.3 W @ 14.5 volts or 1.47 A (manual lists 1.18 A)

license lamps are 9.2 W @ 12.8 V, 11.8 W @ 14.5 volts or 0.81 A (manual lists 0.66 A)

Total current draw is 13.66 A or 11.83 A using the manual figures.

I’ll measure some of these bulbs this weekend and see what my meter reads also.

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1,639 Posts

I had the same problem and it was a pinched wire in the left switch housing.

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I had the same problem and it was a pinched wire from when I installed the PCIII

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Pinched and chafed wires are the bane of these bikes! Everything else is pretty well sorted.

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Discussion Starter · #15 · Dec 15, 2008

Well, no sign of the pinched wire. Rode about 100 miles yesterday with no problems – the high beam mod is great! Thanks for the help – I’ll keep looking for the pinch.

BTW – ran an easy 11.4 1/4 mile (as clocked by the VGauge) with a 3.1 0 to 60. Could have launched way harder and bounced off the rev limiter in 4th.

Bike is running goooood.

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… I’ll measure some of these bulbs this weekend and see what my meter reads also.

I measured current draw for most of these lights using two batteries in series and a 50 W wire wound variable resistor as a voltage divider to regulate voltage. I didn’t measure the license plate lights because they’re a pain to remove and I didn’t have any spare bulbs.

low beam bulb (H11):

4.450 A @ 12.8 V or 56.96 W (manual lists 4.3 A)

4.750 A @ 14.5 V or 68.88 W

high beam bulb (H9):

5.200 A @ 12.8 V or 66.56 W (manual lists 5.1 A)

5.600 A @ 14.5 V or 81.20 W

running light bulb (part of 1157):

0.590 A @ 12.8 V or 7.55 W each (manual lists 0.59 A)

0.630 A @ 14.5 V or 9.14 W each

Assuming the license plate bulb has a 12.8 V rating as indicated in the manual:

0.330 A @ 12.8 V or 4.22 W each

0.374 A @ 14.5 V or 5.42 W each

I’m not sure why the manual shows current draw at 12.8 V. Since the voltage regulator delivers 14.5 V ± 0.25 V @ 1200 RPM, the fuse panel will normally sit at 14.5 V. This means the “LIGHTS” fuse with both headlamps on will carry:

+61404532026 X 0.63 (one tail light and two front running lights) + 2 X 0.374 =

12.988 A @ 14.5 V (12.080 A @ 12.8 V)

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Thanks for doing this. I haven’t had time to check mine, but I suspect the LED running lights give me more headroom for the Headlight Modification.

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Thanks for doing this. I haven’t had time to check mine, but I suspect the LED running lights give me more headroom for the Headlight Modification.

RJ,

Yes, any LED lights would help. The reason I didn’t test the license plate bulbs was because I’m using the HD LED tail light (+61404532026). That light doesn’t pop out as easily as the original light and I didn’t feel like tearing my fender apart just to check those bulbs.

The next time I have the rear fender apart I’ll measure those license plate bulbs as well as the HD LED tail light.

I would guess an LED tail light will help reduce the load by about ½ amp and if you have the front LED running lights that would reduce it another amp compared to incandescent bulbs but it all depends on what LED circuits you have.

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