Blowing headlight fuse

[TheWood]

After noticing my headlight not coming on when the key was turned on my 06' Uly, I checked the fuse to see it had blown. After changing the fuse, it immediately blew again(Duh?) Checking in with you guys for suggestion on my first move. I saw from searching here that I may need to remove windscreen, check the connectors,etc. I guess I'm wondering what the most common reason for blowing this fuse is, if there is one. Bike has 42k miles. I keep the bike on a smart type maintenance charger for the AGM battery and notice that when I turn the key on, the voltage at my "cigar lighter" is at 14.9v with it connected to charger, and when charger is unplugged will slowly come down to 12.7v after surface charge dissipates(holding brake light on for awhile). Is the 14.9v too much to see?

[Barrett]

I've mentioned this several times on here thru the years.....AGM(Absorbed Glass Mat) batteries should NOT be continuously left on a battery tender. And yes...15V is too high of a voltage being read at your power outlet. The 15A headlight fuse blowing could very well be directly related to the high static battery voltage. I have seen this scenario before with a garbage Chinese battery left on a tender...then popping one or more fuses when attempting to power up and start the bike. Before you tear into the wiring harness associated with the headlight circuit....carefully check the quality of your battery and have it load tested.

Then do these checks as follows with known good 15A headlight fuse:
1-KEY OFF--KILL SWITCH TO ON---HEADLIGHT SWITCH TO HIGH BEAM. NOW TURN KEY ON BUT DO NOT START. FUSE OK? HIGH BEAM CIRCUIT IS OK. NOW SWITCH TO LOW BEAM. FUSE BLOWS? PROBLEM IS IN LOW BEAM CIRCUITRY WHICH IS THE YELLOW HARNESS WIRE.
2-KILL SWITCH TO ON----HEADLIGHT SWITCH TO HIGH BEAM---KEY ON---ATTEMPT TO START. FUSE OK? LOW BEAM CIRCUIT HAS SHORT TO GROUND OR FAULTY BULB SOCKET.
3-REMOVE FLYSCREEN TO ACCESS HEADLIGHT HARNESS. UNPLUG SAME AND NOW ATTEMPT TO START. HEADLIGHT FUSE OK? THE PROBLEM IS IN THE LIGHT HARNESS. HEADLIGHT FUSE BLOWS? THE PROBLEM IS IN THE STARTING CIRCUIT.
4-HEADLIGHT HARNESS CONSISTS OF BLACK/ORANGE/YELLOW/WHITE. BLACK IS GROUND..ORANGE IS 12V CONSTANT...YELLOW IS LOW BEAM FEED...WHITE IS HIGH BEAM FEED. CHECK IF ANY OF THE 12V POWER FEED WIRES HAVE RUBBED THRU AND GROUNDING AGAINST THE HORN MOUNTING BRACKET.
5-UNPLUG THE GREEN WIRE AT THE STARTER SOLENOID. NOW WITH KEY ON ACTIVATE THE START SWITCH. FUSE OK? YOU'VE NARROWED DOWN THE PROBLEM TO THE LIGHTING CIRCUIT OR RIGHT SWITCHGEAR STARTER BUTTON CIRCUITRY. FUSE BLOWS? YOU'VE NARROWED IT DOWN TO THE WIRING CIRCUITRY BETWEEN THE START RELAY AND SOLENOID.

Report back with findings.

[TheWood]

Excellent info., thankyou. I thought the more expensive smart chargers made for AGM batt.'s with the desulphuring pulse mode,temp.compensating, automatic,etc. would be ok for this. But I will heed your advice and unplug the maintainer, and instead,monitor the battery in the off season and when not riding for an extended period. I'll charge up only periodically, and as needed. I look forward to performing the steps in your troubleshooting tutorial, and will definately report back with my findings.

[Barrett]

My pleasure Bob and let me know how you what you find. Since this is occurring simply by turning on the ignition switch, you've pretty much isolated the problem to either the battery, left handlebar switchgear where the hi/lo beam switch is, headlight wiring harness, or one or both headlight sockets. Also Bob, highly unlikely it is associated with a faulty KEY SWITCH or ACC relay.
Let me know what you find.

John

[TheWood]

Finally found some time to chase this short down. It turned out to be the two wires coming from the passing lamp switch in the lefthand switchgear assembly. The previous owner retrofitted the grips for heated grips, and when they reassembled, the leads weren't tucked away properly, and were smashed. After several thousand miles of vibration and slight movement of the assembly, this was the result. I cleaned all the internals with electronics spray cleaner, and then was able to simply re-tape since all the copper strands were still in one piece. I consider myself a decent wrench, but wiring has always been my weakness. So thank you John for helping me with confidence to get this done. I'm loving this Uly!

[Barrett]

My pleasure Bob and glad you got it properly sorted and resolved. In your scenario, 99% of the time it's in the headlight bucket area and is always a dead short to ground.

[TheWood]

What I didn't mention is that the headlight bucket is where I started. So now I have all clean connections there, and a better understanding of how it all works.