Headlight failure - low beam at speed - Page 2 - MVAgusta.net
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post #11 of 15 (permalink) Old 08-20-2019, 03:49 PM
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That was one of the first things I thought might be happening since the first few times I encountered it I was wearing winter gloves. However, I have been very attentive to that left hand and I am certain that it is not me that is causing this behavior.

Thank you!

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Originally Posted by esq'z me View Post
I have experienced this intermittently in the past on my 910R and at first was alarmed...but the bike ran perfectly, and the light cam right back on, just a brief flicker off.

And then one night realized my glove was contacting the high beam flash button, and under hard acceleration my grip on the bars tightening would occasionally slightly depress that button...which caused the low beam to go out !!!!

So I quit worrying.
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post #12 of 15 (permalink) Old 08-20-2019, 04:06 PM
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@quixotic_1: Since the culprit seems to be vibration induced failure at a specific RPM, it might follow that the relays in the SPU don't like that vibration spectrum. It is also possible that the SPU box itself is not mounted well enough to prevent vibration induced effects. I would at least start there.

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post #13 of 15 (permalink) Old 08-26-2019, 01:31 PM
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I've experienced it. The SPU was at fault. At high revs, the low beam would cut out. It became very consistent and at lower and lower revs. To test, I put a voltmeter to the socket, revved the engine and the voltage cut out. The low beam relay is part of the SPU. I ended up rewiring the low beam through a relay. The SPU lasted another year until my bike wouldn't even start. After I replaced my SPU, I restored the original low beam wiring and it works like normal.

2007 910R
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post #14 of 15 (permalink) Old 08-27-2019, 12:15 PM
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I am certain that the SPU and its associated wiring are all solidly mounted and connected. I only know this because I have checked, re-checked and then did some work and then checked again.

Given the replies, it looks more and more likely it is the SPU. Fortunately, I have a known good second unit that I can swap in at some point and test. Unfortunately, time does not permit that anytime soon (about to have reconstructive surgery on my rotator cuff, and there are some other priorities: fork re-build, new tires, new chain, etc.). It only happens to me at the high end - never on roads under 50 MPH where I also don't use excessive acceleration - so I can use my high beam while there (no one around here notices motorcycles, anyway, so that helps).

Thank you!

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Originally Posted by silentservice703 View Post
@quixotic_1: Since the culprit seems to be vibration induced failure at a specific RPM, it might follow that the relays in the SPU don't like that vibration spectrum. It is also possible that the SPU box itself is not mounted well enough to prevent vibration induced effects. I would at least start there.

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post #15 of 15 (permalink) Old 08-27-2019, 12:18 PM
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Thank you for providing your experience. It does look more and more that the SPU is at fault. Fortunately, this is my second SPU (the updated version) and I have another known good unit to test with. Once I get some time to do it, I'll do the swap and see what happens. (Of course, should the SPU fail before that, well, I guess I'll be testing it even sooner!)

Also, thanks for the tip on the second relay.

Cheers!

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Originally Posted by moocowman View Post
I've experienced it. The SPU was at fault. At high revs, the low beam would cut out. It became very consistent and at lower and lower revs. To test, I put a voltmeter to the socket, revved the engine and the voltage cut out. The low beam relay is part of the SPU. I ended up rewiring the low beam through a relay. The SPU lasted another year until my bike wouldn't even start. After I replaced my SPU, I restored the original low beam wiring and it works like normal.

2004 Brutale S
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