Author Topic: c10 Headlight - only works when bike in gear and at lower revs  (Read 110 times)

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Offline mwestjeeper

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c10 Headlight - only works when bike in gear and at lower revs
« on: September 10, 2019, 11:50:22 pm »
Ok guys, here is my first post, been lurking awhile and just picked up a 2002 c10.  Headlight only works when i put the bike in gear, and only as i rev it up then i shift to lower rpms it goes out again.  doesn't work however, when revving in neutral sitting still.  seems to get dim and flicker as i get to higher rpms right before shifting too.  only comes on full strength in the lower to midrange, in gear and moving.

there is power at the jbox, fuse is good, and there is around 13.9 volts at the socket when idling.  sure seems like bulb should come on at that point, but it doesn't until i put it in gear and actually start moving / revving.  it flickers when i put it in gear sitting still, which seems even stranger.  it appears to have the murph headlight kit on it, and has a rebuilt jbox.

all other lights work as normal - dash, tail, brake, signals.  seems like if it were alternator related, which might explain the revs, it would light up when revving in idle too?  alternator doesn't behave differently under load, vs neutral does it?  is it some kind of grounding oddity?  but i would think if it were a bad ground, i wouldn't be seeing almost 14 volts at the socket at idle?  tried multiple bulbs, that all test good in other bikes.  I'm at a loss at the moment, doesn't seem to make any sense.

I sure appreciate any help, and while i know all my other bikes inside and out I've only had this one for 48 hours so the nuances are unknown to me...  I figure you guys are going to say "oh, it's that one thing that all c10's do...  :) :)

Thanks again!

Offline MAN OF BLUES

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Re: c10 Headlight - only works when bike in gear and at lower revs
« Reply #1 on: September 11, 2019, 12:28:08 am »
quite to the contrary, this is an "odd anomoly" so, it bears some experiments.   
first off, I think you are spot on with a grounding issue, it's intermittant, and sporadic.. so, starting at thee battery, remove and abrasively clean all of the terminals, and cable ends... then work along th ground path, to insure even and clean shiny metal is making grounds, don't over look the grounding point where the blk/yel wire, grounds to the coil mounting bolt, on the left side coil...
Now on to the J-box; it may have a relay that is failing/intermittant failing, thus it "sometimes works.. might want to contact Larry Buck, here, and have him re-furb those relays.. even new ones can fail, or solder junctions on a single pole of a relay, may create this.. The solder fractures are imperceptable to the naked eye, but doing a careful re-low, and adding some fresh solder, may rectify it.

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW
and if you are gonna call me names... it's MR. Analdweeb if you please...

Offline mwestjeeper

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Re: c10 Headlight - only works when bike in gear and at lower revs
« Reply #2 on: September 11, 2019, 12:35:23 am »
OK, I'll start working through all the grounds and see if that changes any behavior.  It's just odd - it's a rock solid 13.9'ish volts at the socket, sitting there idling in neutral.  In my experience, if you plug something into something at 13.9 volts, the dang thing turns on!

Seems meaningful that it flickers and glows when I pop it into gear with clutch in, and then consistently lights up as I go through the RPM's and cuts out around 5k.  Don't know what it means, but seems meaningful. 

Everything else is rock solid, starts on half a crank, no glitches whatsoever, for whatever that's worth.  Heading out to start digging into grounds now.

Thanks for the suggestion!

Offline cra-z1000

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Re: c10 Headlight - only works when bike in gear and at lower revs
« Reply #3 on: September 11, 2019, 01:07:04 am »
Might be worth it to take a look at the bulb itself . I've never seen it happen but could be a loose filament or the plug and certain vibration levels are affecting it .
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Offline mwestjeeper

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Re: c10 Headlight - only works when bike in gear and at lower revs
« Reply #4 on: September 11, 2019, 01:33:42 am »
OK, just tinkering around with battery, loosening connections and cleaning and jostling things, made it work.  everything already seemed golden tho, so that kinda makes me worry that all i really did was jostle something hidden and loose back into decent connection. only to jostle loose again at a very inopportune moment.  But hey, for now it works and i can take my first ride.

Also weird, that all grounds were nice and clean, and that if it were a funky ground, it wouldn't likely have behaved so predictably.  i.e. light coming on at certain rpms, only in gear. heck if i know.   just one of those haunted gremlins I reckon. 

Thanks!

Offline m in sc

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Re: c10 Headlight - only works when bike in gear and at lower revs
« Reply #5 on: September 11, 2019, 01:39:23 am »
run a committed ground to the headlight from the frame. at least for a test, it sounds like a grounding issue, more than likely self inflicted by the previous owner. .  then look for an unplugged or loose ground connection somewhere. not coming on till its in gear is very, very weird and thats why i lean this way.

Offline JPD

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Re: c10 Headlight - only works when bike in gear and at lower revs
« Reply #6 on: September 11, 2019, 05:38:05 am »
Did you use the head light socket for your voltage testing ground? If not it wasn't a valid test. Like the others, I am going after a ground issue. Start at the socket and work back the harness to a frame ground.