Author Topic: Headlight goes out after 30-45 seconds (Read 3026 times)

mycb750k6 · « **on:** March 12, 2009, 01:41:21 PM »

This is baffling. I start my CB750 76 K6 and the headlight comes on. Hi and lo beam work and then after 30 to 45 seconds it goes out - until I turn it off and let rest for awhile and then do it again. It dims if I rev the engine and then goes out as well. I've cleaned contacts. I can't get at the left hand switch it seems. Hep me, I need a headlight to ride at night.

Spanner 1 · « **Reply #1 on:** March 12, 2009, 03:12:10 PM »

Betcha it's a loose headlight fuse.....see if the fuse is slightly loose in the clips...while your at it shine-up the fuse clips, do the main and tail too ( 5mins. work ! )...then carefully, real carefully bend each side of the clip together so as to put more pressure on the fuse when you 'snap' it into the clip. Sometimes a loose clip over time will heat and become brittle, so be wary with bending them. Good luck.

mycb750k6 · « **Reply #2 on:** March 13, 2009, 11:13:23 AM »

Thanks I tried that too. In fact I went over all my connections with steel wool to clean them up. Doesn't matter if the engine is running or not. When I turn the key on the headlight comes on and then goes out 20-40 seconds latter. Battery is fully charged. Here's a clue. When the light in on, my hi beam indicator light is on too but when it's out, the hi bean light is also out.

Spanner 1 · « **Reply #3 on:** March 13, 2009, 09:50:25 PM »

HI-beam indicator light is parallel with headlight, so if both go out then supply has failed.
The supply is the solid blue wire to the headlight and if the low beam works ( white wire ) then I would suggest...A. it's a bad bulb!!, or B. a corroded/blackened contact in the headlight switch....fixable, but requiring ( beware ) microsurgery when you take it apart1 Good luck.

mycb750k6 · « **Reply #4 on:** March 14, 2009, 04:17:07 AM »

Thanks Spanner - the switch is likely it at this point. When you say ( fixable, but requiring ( beware ) microsurgery ) , is there any picture/ exploded view of this baby before I put on my surgical mask? The problem is these switches are no longer made and I can't find one. I need a headlight I think. Let me ask this. Can the switch electrics from one switch be put into another switch housing? And are the HI/LO beam/horn/turn signal wiring all integrated or can I get at just the HI/LO beam contacts. A picture of this thing would surely help.

Hush · « **Reply #5 on:** March 14, 2009, 04:48:57 AM »

You could easily jerry rig a switch, hey it wouldn't be stock but as you say you need a light.
If like most headlights you have three wires, green (earth) blue (power) and white ? um not sure he he

Kevin D · « **Reply #6 on:** March 14, 2009, 05:57:29 AM »

K6, have you been to the starter switch yet? Theres a trick circuit that shuts the headlight off when using the starter. The headlight fuse draws its power thru that switch.

http://sohc4.com/tiki-list_file_gallery.php?find=&galleryId=9&offset=10&sort_mode=created_desc

mycb750k6 · « **Reply #7 on:** March 14, 2009, 06:39:36 AM »

Kevin, that circuit appears to be for the high beam only. If I have the switch on lo beam, I get the same behavior. Would that starter circuit affect the lo beam as well?

Kevin D · « **Reply #8 on:** March 14, 2009, 07:18:24 AM »

Yep, lo beam also switched off during starting.

From battery > starter solenoid > main fuse > ignition switch > starter switch > headlight fuse > headlight selector > lights > ground

mycb750k6 · « **Reply #9 on:** March 14, 2009, 07:30:34 AM »

OK got it, but the light is on after start - for a few seconds anyway. It's not until 10-20 seconds later that it goes out. Clue is that it dims and gets bright and then dims before it goes out altogether. The darnedest thing is after I let it sit for a while and start it, the same thing happens.

Kevin D · « **Reply #10 on:** March 14, 2009, 08:00:47 AM »

Intermittent circuits are no fun.....got a voltmeter?

mycb750k6 · « **Reply #11 on:** March 14, 2009, 08:28:00 AM »

Yes, are thee some specific tests I should make?

bryanj · « **Reply #12 on:** March 14, 2009, 08:46:49 AM »

Has some PO fitted a thermal link (like a fuse but resets) in the line somewhere?

Spanner 1 · « **Reply #13 on:** March 14, 2009, 08:50:50 AM »

Wow, it is weird ! I think I would start at the bulb and work back....when the light goes out test for voltage on the blue wire at the headlight.....if good has to be the bulb heating/cooling effect..unusual, but! If no power at h/l then test at brown-with-red-tracer,which is the supply to the h/l switch ( it's in the headlamp shell ) Got power?, then the h/l switch is the prob.....no power?, test at h/l fuse ( has same brown/red to it ) no power?, try 'flicking' the start button, any effect ? try this much and report! btw make sure the - lead of the meter is on a good ground. P.S....if you disconnect the green/red at the starter relay you will be able to press the starter button repeatedly without the starter running each time.

MickeyX · « **Reply #14 on:** March 14, 2009, 08:57:58 AM »

it sounds like something is heating up in the circuit. when it gets too hot, it shuts it down. did you actually replace the fuse itself? i know it's a PITA but try to follow the wiring the whole way back to look for a short or a badly spliced connection. the actual switch on the handlebar could be a culprit too. I've found one on a former bike that someone just twisted wires together and put tape on and that was it. when it got warm (near the engine) the tape would soften, slack off on tightness, the wires weren't as tight and it wouldn't conduct. ya never know what ppl do before you own it.

as for the headlight connector, you can use any kind that fits your particular headlight setup, with the same # of wires. just make sure it's a size that fits in the bucket. some are huge, like for cars and big trucks cuz they have the room. then solder it in and put some heat shrink over it.

good luck.

HondaMan · « **Reply #15 on:** March 14, 2009, 09:04:46 AM »

This actually sounds like the filament in the headlight itself has broken. As it heats up, the filament pulls away from the support, opening the circuit.

Here's something to try that can test this: turn it on, leave it on for longer than your "cool down" time that you mention. If it alternately flickers and goes out again, it's in the bulb itself.

Reason: if the high beam indicator stays on at the dashboard, the circuit is still ON, as they connect together at one point. So, it would then be in the bulb.

mycb750k6 · « **Reply #16 on:** March 14, 2009, 09:17:27 AM »

Alright I'm on it. This will take a half hour.

mycb750k6 · « **Reply #17 on:** March 14, 2009, 11:39:52 AM »

Spanner,
Took a little longer than a half hour but your suggestion to flick the starter button was geneous because when I do that I can make the light come back on. Brilliant! So it's a faulty connection in the right hand switch and more specifically the starter button. Is there a remedy for this other than a new right hand switch?

Patrick · « **Reply #18 on:** March 14, 2009, 11:46:37 AM »

You could clean up your starter button. It is only a brass rod that contacts a brass plate (or are they both copper?) to complete a connection. I don't think the button is your problem. I would bet that it is something else that is stimulated when the starter is engaged, like the relay that makes the headlight go out when the starter button is pressed.

Patrick

mycb750k6 · « **Reply #19 on:** March 14, 2009, 11:51:00 AM »

Where is the relay?

Spanner 1 · « **Reply #20 on:** March 14, 2009, 12:03:15 PM »

Genius, no, luck of the Irish, maybe !....when I got my bike, it had laid-up for years, when I turned the ignition on, the starter was engaged and the headlight stayed on...what the heck ?
Well, it caused me to go thru' the whole wiring loom looking for shorts etc., the last thing I thought of was the start button as it was free and not jammed in! You can take it apart, it's a little plastic 'box', 3 wires....two little tabs will release the plate where wires connect..but inside is two sliding contacts which are spring loaded against the plate...all parts are tiny..but a good clean will restore it good...mine has no prob. after two years.. Good luck with it, btw, I tried all kinds of cleaner squirted in there..just wouldn't do it !

No relay involved, when you push the button the h/l contact 'opens' and the starter ( relay )
contact 'closes'.

mycb750k6 · « **Reply #21 on:** March 14, 2009, 01:25:06 PM »

Oh well. I opened the switch assembly and the starter button clear plastic assembly disintegrated - turned to crumbled plastic. Now the starter button doesn't work and the bike doesn't start. Looks like I need to find a replacement.

Spanner 1 · « **Reply #22 on:** March 14, 2009, 01:40:58 PM »

Sorry to hear the switch fell apart...if you don't mind kickstarting the bike you could disconnect the yellow-red tracer in the headlight bucket ( goes to start relay ) and connect black to black-red tracer and headlight will come on with ignition 'on'.

mycb750k6 · « **Reply #23 on:** March 14, 2009, 02:07:50 PM »

Ordered a switch - mucho money. You're right I can kick start it for now and wait for my switch to get here.

mycb750k6 · « **Reply #24 on:** March 17, 2009, 05:13:58 AM »

Spanner

I’m going to try your instructions below but I’m not completely clear on a couple of things.

“Sorry to hear the switch fell apart...if you don't mind kickstarting the bike you could disconnect the yellow-red tracer in the headlight bucket ( goes to start relay ) and connect black to black-red tracer and headlight will come on with ignition 'on'.”

1. disconnect the yellow-red tracer in the headlight bucket – Disconnect from what? What’s it connected to now?
2. connect black to black-red tracer – how are they connected now? Connect them how?

For the rest - sorry for resurrecting this thread.

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Author Topic: Headlight goes out after 30-45 seconds (Read 3026 times)