Topic: CB400F electrical dilemma

[aliengirl]

i have a '77 CB400F and my flasher was acting like it was about to go so i replaced the relay which cured that problem but...
i then noticed that my horn was not working and neither were my brake lights. i checked all the fuses and replaced them even though they looked fine. but, the horn and brake lights are still out. can anyone tell me what else to check at this point? i am kind of an electrical novice and don't know where to go from here. (the battery is fairly new and everything looks like it's getting enough power). many thanks.

[Sam Green Racing]

Not having a road bike that part of the system is alien to me, but is there a chance that when you changed the relay you may have dissturbed another connection..........just a thought.

Sam.

[aliengirl]

yeah, i thought of that and looked over the neighboring connections but didn't notice anything. it could be worth a closer look though. thanks.

[Sam Green Racing]

I am sure someone will come along and tell you how to test for the fault (probably twotired)

All you will need is a small multimeter.

Sam.

[TwoTired]

Okay, the only wire diagram I have for a Cb400f is from an old Haynes Manual.
As a wild guess, I would check the black wire interconnects in both your headlight and the box under the gas tank.

The Black wires are activated to 12v when the ignition switch is on and provides power to both the front and rear brake light switches and feeds the horn (among othe things).
  If you want to check with a mutimeter, the black wire at the horn and the stop switches should have 12 V on them with the ignition on.  If not trace the wires and connections back to the source.
Cheers,

[Bodi]

Most likely is a general corrosion and age problem on the entire harness. My experience is that I can chase problems forever, always something new going weird... or clean and lube every connection in the harness all at once and be trouble-free.
There's a few descriptions of this process in the forums. It sounds like a lot of work (and does take a while) but you'll save time and trouble in the end. If you actually have any "real" problems like bad switches etc, once the connections are fixed up troubleshooting becomes pretty easy.

[Tim2005]

It does sound like a dislodged or bad connection... maybe one off the starter relay... but in any event you'll find the interactive wiring diagrams on this site very useful to learn how each circuit works & connects up:

http://oldmanhonda.com/MC/MC.html

[aliengirl]

thanks Tim. that wiring diagram is very helpful. too bad the yellow ink just went out on my printer! well, a few minutes with a yellow marker and i will be set

i did clean and lube all the connections behind the headlight when i had the front end apart to do the steering head bearings last summer. but, i guess it does sound like a bad connection. well, i'm off to the garage to see what i can sort out....

[gaijin]

If you don't have one already, I would invest in an electrical tester of some kind. You don't even need a multitester, just the light test can be enough for a 'yes/no' answer when checking connections for power.

I'm a beginner with this stuff too but here goes. It looks like the horn and brakelight don't share much. The horn gets power through the ignition switch, and the brakelight/taillight gets power from the the dimmer switch through the ignition switch. I'd check the power at those switches and like TwoTired said, trace the harnass.

Does your taillight still work? Do the tach/speedo lights work?  If you got caught in the rain last week maybe check the ground sfrom the horn switch, and also the taillight/brakelight/headlamp ground.. maybe they're a little corroded.

Also are you the same aliengirl from BARF? It'd be nice to meet some other CB400f owners in SF!  

[Bodi]

Well, there seem to be twice as many wires than will fit in the headlight shell but there are a LOT more connections. The keylock,engine, rectifier, and fuseblock plugs cause a lot of trouble. There's a large wad of bullet terminals under the tank just behind the steering stem. The alternator circuit has a set of bullets under the left engine cover that contribute to many mysterious charging problems.

[aliengirl]

well, i went out and bought a multitester today (it was pretty inexpensive) and i also bought new fuses. when i bought my bike last March it came with some parts including a bunch of fuses but i thought that perhaps using 10 or 15 year old fuses may not be such a hot idea! so i cleaned all the connections in the fuse box and replaced the "old" fuses with spankin' new store bought ones and *wallah* everything was working! yippee!

so, i cleaned the chain and some other odds and ends. then i rode my bike to work and on my way home i noticed that my brake light was NOT working once again but my horn was working fine. and then my turn signal started acting weird again like it was when this whole thing started. it was doing this fast flickering thing instead of a steady flashing signal. quite bizarre.

and yes, the taillight and the tach/speedo lights are all working. i only got caught in the rain very little last week. i keep my bike in a garage both at home and at work so she hasn't gotten wet a whole lot. but Gaijin, you may be onto something regarding the grounding and i will check that out. and thanks for the heads up on all the other connections Bodi. i will try and make friends with them and hopefully figure this out.

i was all psyched at first when it seemed like sucha  quick fix cuz the manual for the multitester was completely unitelligible. eek.

oh yeah, Gaijin- i am the same aliengirl from BARF. do you have  a diff nick there? i don't post there very much but sure, it would be cool to meet another CB400F owner in town (especially someone who knows more about electrical stuff than me!  )

[Mark M]

A 15 year old fuse is fine, some people who post on here are happy to ride on 15 year old tyres! (Dont'T)

Sounds to me like all your connectors could do with a clean out. Get some fine (600 or more grit) and go round every connector on the bike giving it a rub down till nice and shiney. Roll up small strips round matches or cocktail sticks so you can do the inside of female connectors. Make sure you do the fuse holders too. Just work round slowly doing one at a time, it should take 3-4 hours. This should set you up for another 25 years without electrical gremlins. 

[gaijin]

and then my turn signal started acting weird again like it was when this whole thing started. it was doing this fast flickering thing instead of a steady flashing signal. quite bizarre

You know, my old one did this before I replaced it. Is yours an electronic flasher? I didn't have time to troubleshoot the flickering one and simply replaced it with a normal flasher relay (the kind with the expanding and contracting piece of metal inside). I wish I knew what caused them to do this. Hmm...

Also regarding checking fuses, sometimes they can be burned out on the very ends where you can't see it, so: you can pull it and use the multitester to check for continuity, or you can turn on the ignition and check both sides of the fuse for power by setting the tester to 12v DC, putting the positive terminal on the fuse end, and the negative on a nice chunk of frame to ground it. I pull em, but I guess flipping the ignition and using the power can be faster.

Anyways, glad you got most of your problems sorted. My name on BARF is the same as here, but I don't really post much there. More of a lurker really. But your name came up when I searched for CB400f's    I'm pretty insane for these bikes... I'm loooking at getting a third 400f, since two wasn't enough already. Two parts bikes, woo! Hopefully I'll get one bike running from the two incomplete ones. 

[aliengirl]

now everything is working again! well, my blinkers are still doing that flickering thing but it still may count as working (in a way!). i haven't had time to do any further electrical cleaning or snooping. but, how can i tell whether my flasher is electronic or the other kind? it's just one of those 12v Emgo replacements i picked up at Charlie's Place - which is where i will have to bring my bike soon if it starts going wonky again before i have time to figure it out myself. oh well.... i'm still gonna go throught all the wiring and do a general cleanup when i get a few hours.

[Vagelis]

Goodmorning, what you should do with your flasher is simple. Check the wattage of your bulbs in your turn signals and the wattage stamped on the flasher. Our old bikes had 21W or even 18W bulbs for the turn signals. Todays bikes have 23W bulbs. So if the flasher is for 23W bulbs it starts acting wierd.
Ride safely, Vagelis.

[Bob Wessner]

Sounds to me like all your connectors could do with a clean out. Get some fine (600 or more grit) and go round every connector on the bike giving it a rub down till nice and shiney. Roll up small strips round matches or cocktail sticks so you can do the inside of female connectors. Make sure you do the fuse holders too. Just work round slowly doing one at a time, it should take 3-4 hours. This should set you up for another 25 years without electrical gremlins. 

After cleaining each connector, put a dab of dielectric grease on the male side before you push them together. This will prevent. or slow, future corrosion. You can get a small tube at any auto parts store.

[SteveD CB500F]

I've often wondered why we advise people to use dielectric grease rather than conductive grease for the wiring..

So I Googled it and here's the answer:

Dielectric vs. Conductive Grease to Protect Connectors and Grounds.

[Query:] You have repeatedly recommended the application of dielectric grease to underhood wire connections. Isn't the insulating property of such grease counter to the goal of IMPROVING the integrity of electrical connections? I would think that a conductive paste (such as Eastwood's Kopr-Shield) would be better. The only potential downside I can think of is that sloppy application could cause short circuits, but care and common sense should preclude this.

[Response:] This is a good question and one that I have received several times. Yes, it is true that the dielectric grease is non-conductive. However, in the context of connections that carry voltages larger than 1 volt, the grease will not result in a bad connection. The male and female connectors will wipe enough of the grease off at the mating surface so that the electricity will flow just fine. The important part is that there is no chance of the grease creating a conductive path between adjacent terminals in a multi-terminal connector. The main purpose of the grease is to seal the terminals against oxidation which creates a high resistance barrier and moisture and dirt which can result in shorts and ground paths.

[aliengirl]

well, i didn't have time to investigate any further so i took her into the shop today and here is what the problem was...

the relay was a 6v rather than a 12v (i had asked for a 12v but didn't check the box which looks exactly the same- o well!). also, my mechanic said that that 23w/18w issue is just not true. then she went on about the dang internet and all the misinformation about bikes and stuff- which was really funny.

as for the other electrical maladies, the fuse box was kinda melted away in the back so the fuse holder for my taillight was being kinda mobile and causing all those intermitant problems. so, i have an inline fuse now and everything is working all fabulous again. yea!