Topic: Headlight goes completely dim w/start button pushed.

[750K8 Kev]

Is it normal for my headlight to go very dim for the duration that I hold my start button? 

I am trying to diagnose a charging problem and just want to see if that's normal.  I'd imagine it would go dim a little, but mine goes off.  My bike hasn't been starting unless it's fully charged, even kickstart.  I drove it around yesterday for about 45min, first 45 minutes on a bike on the road ever!!! woot!  When I got back I let it sit for about 20min, it shut off and wouldn't start .  I just ordered a used rectifier and regulator, hope that solves my issue.  My rectifier harness is fried.

[Spanner 1]

Your headlight MUST go off when you press the start button as that is the design. Headlight goes off to reduce the load on the battery which is 'stretched' just cranking the starter motor.
If the rectifier wires are fried = rectifier fried = no charge.... prob. jumpstarted with + and - reversed, pretty common and always done by the previous owner... 

[750K8 Kev]

Your headlight MUST go off when you press the start button as that is the design. Headlight goes off to reduce the load on the battery which is 'stretched' just cranking the starter motor.
If the rectifier wires are fried = rectifier fried = no charge.... prob. jumpstarted with + and - reversed, pretty common and always done by the previous owner... 

Thanks! asom had a thread back in May where you helped him diagnose a very similar sounding issue, I hope it works out as well as his!

[BJ2001]

new here...did a search and found this

seems related.

My headlight just went OUT at the same time that my starter went out...press the starter button and...NOTHING...doesnt make a sound.

However, if I hold the starter button in, the headlight actually comes on...goes off again upon release.

While I don't care much about the electric starter, i need the headlight.

Couldn't figure out why the headlight is tied into the starter somehow.

So what do I need to take apart and fix (its okay to talk down to me like a 4 year old...in fact, given my mechanical skills, its preferable)

Thanks in advance

oh yeah, 76 cb400f

[Roach]

i would take a run through your wiring harness look for any melted wires. take your head light out of the bucket look in it for melted wires work your way back to your fuses and battery might be something simple as melted or a not fully connected connection.

[HondaMan]

new here...did a search and found this

seems related.

My headlight just went OUT at the same time that my starter went out...press the starter button and...NOTHING...doesnt make a sound.

However, if I hold the starter button in, the headlight actually comes on...goes off again upon release.

While I don't care much about the electric starter, i need the headlight.

Couldn't figure out why the headlight is tied into the starter somehow.

So what do I need to take apart and fix (its okay to talk down to me like a 4 year old...in fact, given my mechanical skills, its preferable)

Thanks in advance

oh yeah, 76 cb400f

The START buttons are frequently corroded on these bikes, from years of sitting. They need to be cleaned to improve on this situation, and if they are used more often they will work better. Don't use a halogen headlight with the 400F and this START switch, as it will slowly burn the contacts (like the 750 and 550 bikes do).

You can often clean the switch with electrical contact cleaner or CRC Brake Cleaner: spray some in, work the switch a number of times, repeat as needed (at least 3 times). It will work better for a while, then you'll have to repeat this process a couple more times over the year before it will become reliable again. Operating it will slowly wear away the corrosion it now has.

The switch is unobtanium now. Disassembling and cleaning the switch itself, with reassembly, is possible, but not for the impatient of feint-of-heart, as it is VERY hard to reassemble. 

[BJ2001]

well...the START button WAS working with no problems at all...then suddenly....NOTHING...so I thought I must have a blown fuse...

fuse replaced...nothing.

thats when i noticed the headlight comes on WHEN i press the button.

this baffles me.

so the headlight gets power...so its not the bulb obviously...but only gets power when the button is pushed.

which in turn tells me the starter button is getting power.

as for looking at the wire harness all the way down..ouch...i mentioned my skill level...do i have to open up the whole wire harness?

[BJ2001]

doing some reading and may have discovered a problem.

i may have started with high beams on...apparently thats no good.

[TwoTired]

well...the START button WAS working with no problems at all...then suddenly....NOTHING...so I thought I must have a blown fuse...

thats when i noticed the headlight comes on WHEN i press the button.

this baffles me.

Check out the wire diagram (NOT the Clymer).  The 400's starter switch turns off the headlight while the starter is engaged.   These switches frequently disintegrate, making their functionality a random affair when the button is pushed.

Cheers,

[bollingball]

TT are you getting frustrated

[TwoTired]

TT are you getting frustrated

With what?

People with selective hearing, perhaps?

[vames]

Sorry to be a bit dense, but can anyone explain the mechanism at work here with the light going off when the starter button is pressed? I can't see it in the diagram -- what actually cuts the light off? Is it in the switch (something opens when something closes?) or at the solenoid or what?

(my headlight won't go on at all right now with fully charged battery and working starter and all -- I want to know if I should test anything in the switch.)
 
Thanks.  

[bollingball]

vames What bike do you have? They don't all have the headlight cut out circuit. Did you download the manual with the Electrical prints? If not do and study it then report back. It's a simple little circuit. You need to break down the individual circuits. The main idea is to turn off the headlight while trying to start to save power for the start & run system. The battery only has so much power.

[DarcyCB400F]

When my 77 CB400F had a faulty starter switch, the bike would start but the headlight wouldn't light. Because the starter button would actually stick in the depressed "start" position, I would have to pull it back out to prevent the starter from running even though I quit pushing it.

I took the button apart to see what was the matter only to have a million little pieces in my hand because the internal plastic housing that held the starter button guts was totally disintegrated. Upon a closer inspection, I figured out why the headlight wouldn't light.

Because the power for the headlight runs thought the starter switch, and because the starter switch was FUBAR, I couldn't get the headlight to light so I replaced the switch with a "Made in China" Honda original (NOT) starter switch.

Here is how it's made to work as best as I can describe it. There are two contact points separated by a "bridge" that the starter switch rocks on. Think of a school yard teeter tooter... I believe the "bridge" is a ground which the "teeter tooter" starter switch uses to complete the circut. When the starter button is at rest, it completes the headlight circut until you push the button which interupts the circut to provide full power to the starting circut. Assuming the bike starts, releasing the button restores power to the headlight.

In short, I believe your starter switch has had the same fate as mine; it has disintegrated to a point where your switch is FUBAR.

I have an owners manual wiring diagram I can email to you that is 100% accurate for your 400! Just let me know!

I hope this help!

[phil71]

When you're working thru electrical issues on these bikes, keep in mind, honda designed the most functionality with the fewest contact points and fewest leads. Almost all the time, the simplest solution is the right one. So troubleshoot with the easy stuff first. Dirty contact, old switches etc.. don't get into the actual wires unless you can see that someone went there first.. in which case, the elegant simplicity honda built into it is out the window.

[TwoTired]

Sorry to be a bit dense, but can anyone explain the mechanism at work here with the light going off when the starter button is pressed? I can't see it in the diagram -- what actually cuts the light off? Is it in the switch (something opens when something closes?) or at the solenoid or what?

(my headlight won't go on at all right now with fully charged battery and working starter and all -- I want to know if I should test anything in the switch.)
 
Thanks.  

Some SOHC4's don't have a headlight cutout with application of starter button.  I think those usually have a separate lighting switch, at least in stock form.

The bikes that do, have a rocker bar in the switch behind the push button.   The center of the bar connects to black (switched hot).  The bar is spring loaded so one end of the rocker bar normally contacts the headlight circuit making the headlight illuminate.  When the button is pushed, the rocker bar breaks the headlight connection and makes the other contact to activate the starter solenoid.

Pity you didn't tell us which bike you have or what diagram you are viewing.

Cheers,

[vames]

I'm even denser than I thought. It's a 75 CB400F. It definitely has the headlight cutoff, so I guess the switch could be one culprit. I've tried to find a factory manual for it, and all I can find is the one for the 350F/400F that doesn't seem to show it (see pic below) -- If I'm reading right, this one shows a headlight on/off switch, which my bike doesn't have. Of course the other wiring diagrams don't show it either.

I haven't had a lot of time to look at it, other than to check the bulb. Now that it's thawed here I'm going to take some time this week, so this gives me one thing to look first before I start textbook troubleshooting the whole circuit. Thanks.

[vames]

OK -- different diagram in the same manual. I believe this is it.

[CBDee]

Take a look at this for information

http://forums.sohc4.net/index.php?topic=80532.0

[vames]

Very helpful -- for some reason I never saw that post in my searching.

[750K8 Kev]

Very helpful -- for some reason I never saw that post in my searching.

wow, I totally forgot about this thread! turned in to a pretty good discussion.  I went ahead and just installed a toggle for my headlight.  I had to do this because of the racing switches I installed.  I have a headlight toggle, with a key switch toggle(no key) for ignition, and a nice rubber push start button.  I was limited on poles for the push button, so I had no way to run back for the headlight relay.  Cool switch got of JEGS, had to modify it a little so it could mount on my old breather mounting tabs. I added the hl toggle where the red light would go. http://www.jegs.com/i/JEGS-Performance-Products/555/11001/10002/-1?parentProductId=763172

[cobra2411]

Don't forget to check grounds... Anytime I have an electrical problem that makes me go "How the F is that happening." I check grounds.

Also as a though, to add the headlight off functionality to a switch that doesn't have it couldn't you hook up a relay and use the 87a (normally on) terminal to power the headlight and trigger the relay off the starter circuit?

Wire the stock headlight feed to the 30 and out 87a, ground 85 and tap into the feed from the starter button to the solenoid and send that to 86. Leave 87 open. Actually you could run the starter switch on the handle bars to 86 and hook 87 to the solenoid. Then you just need a simple momentary on switch and your headlight will automatically go out when the starter is engaged. Yeah you will end up triggering the starter solenoid off the stock headlight circuit but it shouldn't take much current to work a solenoid.

[Jonm99]

Not sure if 8 year threads get answered 

Anyway, I have a replacement switch without the headlight cutoff feature and was thinking about doing the same thing with the relay between the switch and the solenoid. On option #2, where if I understand your suggestion, solenoid in /starter button on 86 and feed to solenoid on 87, why would you need a momentary on of the headlight? Wouldn't it switch on as soon as the ignition is opened (and of course momentarily cutoff upon start)?

[Don R]

 If you really want a challenge, buy a European right control and headlight with off/park/on and figure out how the Honda harness works. (the usa bikes are jumpered under the tank) I've owned three 400F's and haven't found one with it's original headlight switch intact.