Topic: CB400F I hate asking for help, but headlight out & my weak point is electrics

[jeff kushner]

Guys,

 I've been occasionally riding my '76 CB400F since restoring it last year or so. It runs like a top...then one day, the headlight goes out, or doesn't light.....I just noticed that it wasn't on. Neither hi or low beams work, nor does the hi beam indicator in the cluster even though I have verified that the bulb is fine. Everything else works perfectly, everything. The turn signals, starter,tail and brake lights, neutral light....everything except the headlight.

I spent the better part of three hours puttering with it yesterday and am still stuck. At the headlight bucket joint light Blue-bl/lt bl ....I have 12 V on the light blue feeding the connection. I plug in the two blues, (one goes to bulb, other goes to cluster). I have 0 on the white and 0 on the green. Between the blue and white I have 5V-6V. Even running a direct ground from green to ground, the high beam does not light?

Any help would be greatly appreciated, obviously I need it!

jeff

[Bodi]

The light blue wires are not the headlight circuit. Dark blue is high beam, white is low beam. The high beam indicator has a blue and green wire to it. The left switchpod gets HEAD fused power on the Bk/Y (black/yellow) wire, and sends it to the high (B=blue) or low (W=white) filament in the lamp. The HEAD fuse gets power from the starter button, this gets key-on power (Bk wire) and, when not pushed, passes it to the BK/R (black/red) wire going to the HEAD fuse. It disconnects the headlight when pressed, presumably to provide more power for the starter motor and ignition during electric start.
"No headlight" is usually the starter button switch, the HEAD fuse or the clips for it, or the connections inside the fuse box. Or some bad bullet connector in the harness.
Measure DC voltage from ground to the HEAD fuse clips with the fuse removed: one end should be battery +12 when the key is on. Using a test lamp may be better than using a meter, a bad connection can read good voltage but won't pass enough power to light a signal bulb. With the fuse installed both ends should have voltage. Check that power is getting to the Bk/Y wire into the switchpod (this harness connection is under the tank, switchpod wires don't come to the headlight bucket). I expect you will find the problem is either the starter switch or the fuse/fusebox. You can eliminate the starter switch by plugging the Bk/R harness wire connector meant for the right switchpod into any open black terminal, the harness wire should be a male and there should be a triple female black with an open connection. The Bk/R wire from the switchpod will be a female, this will be left unused. The headlight will now stay on during electric start but that doesn't seem to make starting any less effective.
Cleaning the fuse clips where they touch the fuse, and the fuse ends, may help. Inside the fusebox (remove it and the back pries off) can fail from overheating, the wires must be firmly soldered to the clips: if any wiggle around then the connection is bad. Resolder or (preferably) replace with a modern minifuse fusebox - you can get ones that mount and connect just like the original.
Get (download) a Honda wiring diagram (not Haynes, Clymer, or any colored website one) and try to understand it. It will be worth the effort. The switch function blocks are confusing but they do make sense and only the Honda diagram includes everything on the bike. If you download a copy that isn't readable, keep looking: there are high quality scans to be found where the lettering is clear.

[jeff kushner]

Yesterday, I removed the fuse block and removed the cover off the rear and verified that both the wires were firmly soldered to the block and that I had voltage on both side of the fuse with it installed.

In the headlight shell, there was a light blue wire (male) connected to a 2-female/1-female on the opposite side. Next the the light blue male, there was a dark blue male that went to the cluster high-beam indicator. On the opposite end was the blue wire going to the headlight bulb. This was the original stock setup when I bought the bike and I highly doubt the former owner, who was the original buyer, had ever opened the shell as he was very lost with anything beyond putting gas in the tank<LOL>. I suppose there is that chance so I don't want to exclude any possibility at this point.

It was working one day, then not the next and I had made no changes in anything.

I appreciate the help very much guys so I will follow your advice and check voltages this evening. I'm also guessing that it's either the starter switch or ignition switch but I don't know how to test them. I removed the right side handlebar controls yesterday and sprayed some contact cleaner in there but didn't do anything beyond since everything seemed pretty well hidden from access!

jeff

[harisuluv]

Don't be afraid to ask for help!  Easy to post a quick question and there are plenty of people that can and are willing to assist quite promptly.  Electrics are certainly not my strong suit either!

[Don R]

Bodi posted one of the most well thought out answers ever. It's hard to add anything except you can get a new right control or install a small switch where the start button is.

[strynboen]

light blue/orange,, are turn signal.(.there is also a blue vith vhite stripe..ve dont use in Europa)think it are somthing drive light in turn signals ilegal in europa

[jeff kushner]

Yes Strynboen, and I appreciate his clarity as well as the other suggestions by Calj, Don and yourself. I didn't get a chance to get into it last night since I didn't get home till bedtime but hopefully this evening, I'll get home in time to go out to the garage to "play" a little. I think that I may have a little reorganization to do in the shell since there was definitely a light blue "hot" wire feeding the connection with the two dark blue leads...one going to the cluster and the other to the high beam.

The signals work but one blinks a little faster than the other which I had attributed to a possible bulb wattage difference but after re-reading Bodi's explanation and your note about the blue/orange being turn signal leads again, I may have one of the turn signal leads feeding the high-beam connection and the other turn signal lead feeding both turn signals(front I think)....of course I'm guessing from memory. I'm usually the one offering help so I know it's gratifying to hear the results so once I get it sorted, I'll post the results.


I'm not a "loner" but can usually find the answers I need by searching so that's why I hate to ask for help...well, that and a heaping helping of bullheadedness too I suppose. 

jeff

[jeff kushner]

 Thanks so much guys....you nailed it Bodi....starter button switch. I was also mistaken about the light blue wire....yes, it is a little lighter than the dark blue but there was a big difference between it being a little lighter and "light blue". My wiring is stock and correct and a little well placed contact cleaner directly at the starter button with the cables removed to make access possible, and the headlight "magically" lit right up!

I'm going to go button it all back up but when the light lit up, I wanted to be sure to say "thanks"!

jeff

here's a couple pics of it just before I took it out for a ride! Every single nut and bolt is original except for the muffler because I couldn't find a NOS stock muffler anywhere...it's fun little bike!

[strynboen]

uh very nice bike,,,Honda just got it total right vith this..SMAll bike..i got 2. 1 running ,and one as reserve /parts

..all this small parts as head light spedometer rpm meter ..alll a bit smaller then all other bikes..it almost a model machine..and a hell lot of charme in it...

[jeff kushner]

Thanks Strynboen, it's a blast to ride. Although I'm 6' tall, I've always liked smaller, lighter bikes, as you can ride them hard without wearing yourself out.

With it's amazingly smooth, linear power delivery, you never get the punch of power that my H1's and H2's produce and can sometimes present problems if your fully leaned in a corner and have misjudged a gear but it's 10,000 rpm redline gives you plenty of latitude too.

I've been riding since 1973 and have always thought that you can have more fun on a small bike at 60mph on a twisty road as you can on a big bike at 140 on a straight one.

Honda did get "it right" with the 400F....yes, I wish it had a bit more power but it's the little jewel of my collection because to me, it just looks perfect!

Thanks again for all your help guys,

jeff

[strynboen]

yes 400 need a bit more power...thats vay they make"ed the 550.

..it have not the charme of the 400...but drives perfekt..in a total balance of vaight and steering kontroll and comfort..i have often thorth of putting a 400 tank and hardvare, on my 550...but then..i like them as stock as possibel..only vith small thangses /upgrades..

[jeff kushner]

 It's ironic that back in the 70's, I scoffed at the cb400f....sure it could turn but it had no power, was no match for my highly modified two stroke bikes at the time.....as soon as we would get a bike, we would begin to "make it better".....now, 40 years later....I'd hate to think how much time and $$ I've spent restoring modified bikes back to stock<LOL>!! One of the criteria I use when deciding to buy or not has to do with how much I will have to "un-do".

Yes, I still build and enjoy modified bikes....my 74 H2 is almost too much for the street and I'm very nearing completion(mounted the cylinders & 34mm flat-side carbs yesterday) of a 75 H1, both have spent plenty of time in my shop being ported for more power, I modified my Yammy 650 turbo to run 18PSI and is no longer the pig it was with the stock 9-11PSI.....but the bikes I really cherish are my completely original bikes.....it sure is funny how that works huh?


jeff