Headlight going dim while accelerating - BMW Luxury Touring Community
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post #1 of 10 Old Mar 27th, 2019, 8:32 pm Thread Starter
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Headlight going dim while accelerating

While “going through the gears” this evening headlight dimmed all the way to completely out but would brighten to normal when getting out off the gas. Alternator? Relay? Capacitor?
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post #2 of 10 Old Mar 27th, 2019, 8:55 pm
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Re: Headlight going dim while accelerating

How old is your battery. If it is in poor condition for what ever reason it could be loading down your system. Something is. Take your volt meter. hole it to your battery terminals and take a reading, now start the bike. Does it stay above 9.5 volts while cranking. Does it read 12.4 or 5 just sitting there not running? Does it read 13.8 or more at idle? these are the good readings. below this no good.

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post #3 of 10 Old Mar 27th, 2019, 10:22 pm Thread Starter
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Brand new battery. Replaced last week after a rear seal/clutch replacement.
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post #4 of 10 Old Mar 28th, 2019, 3:59 am
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Re: Headlight going dim while accelerating

Sounds like an earth problem to me, especially as you have had recent work.

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post #5 of 10 Old Mar 28th, 2019, 1:22 pm
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Re: Headlight going dim while accelerating

Yes, need to check wiring but still do the voltage measurements to be sure your new battery is ok. What a pain, all that work and now another hassle.

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post #6 of 10 Old Mar 28th, 2019, 3:35 pm
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Re: Headlight going dim while accelerating

Flickering lights and headlight going out could be the load shed relay ground point through the starter. There is a single bolt that connects the starter to the transmission. The rest can be isolated by O-rings. Look here and check this bolt for tightness or even missing. If this is tight, then check other earth problems as suggested. You can see it by looking in front of the battery under the back of the tank with a good flashlight.
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post #7 of 10 Old Apr 3rd, 2019, 4:36 pm
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Re: Headlight going dim while accelerating

Mine was doing that back in 2014 when I bought it. Someone else pointed me at this grounding bolt on the starter, and sure enough it was loose.

After about 3000RPM the head light would be flickering, mostly off, the dash lights and gauges would start freaking out etc. I don't recall what size the hex key was, but I cut down one short enough to get it in there. It was still a battle to get my hand in there to turn it, but it was better than the tear down that would otherwise be involved to tighten it with a normal wrench. Last year when replacing brake lines and changing the brake fluid I checked it and it is still tight.


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Originally Posted by bmwcoolk1200 View Post
Flickering lights and headlight going out could be the load shed relay ground point through the starter. There is a single bolt that connects the starter to the transmission. The rest can be isolated by O-rings. Look here and check this bolt for tightness or even missing. If this is tight, then check other earth problems as suggested. You can see it by looking in front of the battery under the back of the tank with a good flashlight.
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post #8 of 10 Old Apr 3rd, 2019, 8:56 pm
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Re: Headlight going dim while accelerating

Daddy told me to look for the obvious answer first. It was almost always that. So I suggest grounding issues, because you just had work done on it. Run an extra ground wire if you are testing and see if that stops it.
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post #9 of 10 Old Apr 3rd, 2019, 11:55 pm
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Re: Headlight going dim while accelerating

Dads are cool, I under rated mine for various reasons and regret it now.
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post #10 of 10 Old Apr 4th, 2019, 8:18 pm
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Re: Headlight going dim while accelerating

You can get access to this bolt which is in front of the battery holder and down very low . . .

John Zeiler helped me years ago @ Ironhorse Cabins with a ball type allen on the end of a screw diver.

Fixed the problem and when I got home got better access to the bolt by cutting off an allen wench

In any case it is very difficult to get access to - remove battery for starters and good luck!!


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