Topic: CB400F short / ignition / wiring madness

[newbhampshire]

I purchased my first bike, a 1975 CB400F, last week, and have been trying to make sense of some ... modifications that are PO curses. I feel it all boils down to an aftermarket ignition switch (where you turn things on, the key fits in, etc). And I've tried to do my research before posting, so bear with me.

The bike runs, or ran, until this. While rebuilding the highbeam switch, repairing a cracked clutch grip, and diagnosing an unlit right blinker, I logically disconnected the wiring. The keyed switch has only two wires: black and red. This leaves the doubled-up brown wire with a male stock plug on it, and a brown/white wire, which was cut down and waving naked in the wind.

The 2x brown WAS wired into something, but I don't know what. Now when I try to start, I am blowing the Main 15A fuse, every time, 9 so far. My inclination is to buy a more appropriate starter switch, but it DID work, and it should again. It is possible there is another short someplace, but not likely at this time.

Also, maybe related, there was a short jumper connected to a brown lead from the main harness and I can't figure out where he went either. All of this is due to both naivete and partial colorblindness -- assuming all colors would match to corresponding colors was foolish, especially since I wad just going to have someone with better eyes help me fix it all. I'll take any tips or tricks; I've located 6 different wiring diagrams and they all assume things weren't monkeyed with. Thanks! Pete

[bollingball]

This is going to be a tough one. First off instead of trying to look at one big problem you need to break it down to individual circuits. For example look at this interactive print
http://oldmanhonda.com/MC/wiring750K1.html
Now go to the next page and look at the strip of green and pink If you click on the pink side it will turn off a circuit turn them all off but one to see how it works
Ken  I will be back

[bollingball]

Now you can turn them back on by clicking the green. You need to decide what circuit you want to work on first. Stay focused on that one until it works. If I were you and to get the most help I would get the correct Sw. The only way for someone who is not there to help is if you agree on what print you want to use. Like both people having the same map. I'm sure others will chime in to help and so will I so pick a circuit and the print for your bike think about the key sw. And tell us what you want to work first. Is this fun or what

Ken

[camelman]

The rear turn signal wires can get pinched and tear through the insulation.  If they do, then they'll short and blow your main fuse.  Since you mentioned a turn signal issue, it wouldn't hurt to look over the wiring under your seat.  Might as well check all the wiring behind your headlight too just to make sure the insulation isn't torn and everything is connected correctly.  Also, get a new ignition switch!

After the above items, I'd start by disconnecting all the green wires (ground) and checking all the other wires with an ohm meter to see if they are shorted to ground.  I got a little lost with everything you wrote though, so there might be a more simple path.

[Bodi]

You're looking at some parts of the harness circuits that are ignored on every wiring diagram except the official Honda one, you should be able to find a readable online version. The printing is very small and some are too blurry to read but there are high def scans.
The short jumper to the brown wire just goes to black, assuming it is at the connector bundle under the tank. This jumper bypasses the nonexistent headlight on-off switch removed when always-on lighting was legislated. Honda added the jumper in switchpods installed in affected bikes but replacement units with this jumper have always been difficult to find and are now impossible to find: you just add that jumper and the tail light works, without it there's no tail light except in "PARK".
The ignition switch wiring is also weird I suppose. There are two tail light contacts, TL1 and TL2. One goes to the TAIL fuse in the fusebox, eventually powering the tail light through that jumper when the keyswitch is ON. The other goes directly to the tail light, powering it from the MAIN fuse when the keyswitch is in "PARK".
Anyway, all this is shown in the Honda wiring diagram - not in any other. I guess it's easier to ignore than try to explain.
As a rule the harness connectors absolutely only connect color-to-color. Adding aftermarket stuff breaks that rule: for example, signal lamps often use black for ground and red for power. Faded dirty wires and some color blindness is a recipe for mistakes. Light blue and gray look pretty much the same to me except in bright full spectrum light: under some fluorescent lights they are indistinguishable.
One good trick for figuring out butchered harnesses is to disconnect all black wire bullets. Use a signal lamp bulb in place of the MAIN fuse, a bit of soldering is required to attach wires to the bulb but it's pretty simple. Then just snap a blown fuse in to clip the wires in the holder.
The turn the key on and connect the bullets one at a time. If a circuit is shorted the lamp will light full bright. If there's a load then the lamp may glow a bit or be fairly bright, but not full bright. The headlight will get it very bright but you'll see the headlight also on fairly dim as well.
Good luck! This is actually a pretty simple wiring system, divided into several sections that can be troubleshot independently. It's daunting when yo look at the spaghetti diagram but with a bit of looking and thinking it will all make sense I think. Every connection, switch, and load is shown in the Honda diagram.

[newbhampshire]

Thanks to all for the advice, I especially liked the interactive chart, which was def. helpful. There may have been a short somewhere on the ignition switch itself, but I tore it all apart, replaced some wires, heat-shrunk all bare connectors, and got that part ironed out. Next was lights, and I determined a few things there, even my original turn signal issue. The single brown wire coming from the harness jumped back into black as suggested, and that gave me my tail marker.

Two problems remain. One is that the brown wires originally heading to the stock switch still have no homes, and they definitely used to (which also feeds 12V incidentally). The second problem is that I have no juice in the headlights, neither blue nor white. I feel like this has to be related to the errant brown set, which could be resolved by a new ignition switch.

I partially understand what the headlight hack was all about, but how was it implemented? If I run the double brown to black, nothing seems to happen, same for dk. green. If I run it to almost anything else, I short the fuse.

So, brilliant fellows, do I have one problem or two?

[Doctorlumen]

Those errant brown wires (as opposed to the one in the headlight bucket that goes to black) used to go to the stock ignition key set. On the Honda diagram, they are noted as "Br". One of them,if I'm hearing you right, should have a white tracer on it, and power all the dash lights, and the plain brown should travel back to the tailight.
Wait....actually, there is a brown wire with a blue tracer...that wire should terminate into black in the headlight. The plain brown, in my diagram anyway, just hangs out. Nothing plugs into it. Like maybe an auxiliary connection or something. I don't know what.

Sorry if this isn't any help at all. But brown for sure powers the tail from the mainswitch, brown/white the dash lamps, and brown/blue goes through the fusebox and joins black. Life will be much easier with that stock (or replica) keyswitch.

 

[Bodi]

The plain brown in the headlight shell is that parking light business again, some markets have a small lamp - like an instrument lamp - in the headlight for a feeble white light that comes on in "PARK" and probably with headlight on as well.

[newbhampshire]

I know its been said, refer only to the original official Honda guide for wiring, and I think I see why now. I kind of resolved some issues and not others.

1) No more blown fuses, but the headlight doesn't work anymore at all. What to do? Check switch I had rebuilt and make sure things operate correctly. They do, but this exposes white, blue and a black/yellow wire, which I assume is the power-positive for the headlight? Why the hell do three other diagrams not have this wire mentioned? Nonetheless, it's either pos or neg, but I can say that it gets no voltage when power is on, though I didn't check when the engine is running.

2) I haven't replaced the ignition switch yet because I did some testing with switches instead... Black and red are the only effective combos at this point, and allow me to start the bike.  Which begs, what is the brown + brown/white combo for? There are two standard switch positions, one featuring red+blk, another feat brown+brn/white. The second position has just red+brown.  The question is, whats the likelyhood this is related to my headlight issue? Since black+yellow doesn't appear to be on the front-end harness, what am I missing? Where's the beef? (And yeah, fuse is fine and I checked the tabs and they're clean-ish)

Through all this, somehow I gobbed up one of the battery cells, so I'd also lost cranking power. Topped off with distilled, bought a trickle-charger, and it's cooking in the kitchen. 

Any other clues y'all can throw would be helpful... I appreciate the input so far, and I promise to make notes for the next owner when the time comes, explaining what I did to 'fix' the previous owners 'fixes'.

[Doctorlumen]

Red/Brown? Like red with a brown tracer? 'Cos that don't make no sense! No 400/4 I have ever seen has had one of those.

If you were trying to check 12v between red and brown, then you need to have that keyswitch on to register any voltage between 'em.

The Black/Yellow wire and the Black/Red wire are both power to pods and thus power to things like the headlight and turn signals I believe. I have never come across a diagram that didn't have those Bk/Y, Bk/R wires...unless its a 350/4 diagram. So double check. Or, maybe you have pod switches off a 350...which I do and prompted me to rebuild my harness.

A far more knowledgeable and eloquent typist may word this better than I, but here goes anyway.
The striped wires, in general, should be the POS charge to the various components. Br/W for example is power to the dash lights, Gr/Y power to the brake lights. The power "send" circuit, if you will. (I have done a bit of sound engineering...syntax is everything.) These components will almost always have a black wire associated with them. The headlight is the wild card here, as it has 3 solid color wires: White, Blue and Green. But, Both white and blue wires feed from the left handle bar pod, thus are powered by Bk/Y. So if that wire is hanging out, then it for sure will fix your headlight problem.

I absolutely agree that the amount of wiring for this bike (all the browns and the millions of greens in particular) seem excessive. Lots of redundancies to be sure. But, if you get ahold of a factory diagram for your bike, and work one system at a time, you'll have your electrics sorted in no time. Be meticulous and study the diagram. Good luck!

[Bodi]

In the 70's Honda went to a multiple fuse system, until then bikes only had one main fuse for the entire harness. With one fuse, a problem with anything electrical would leave you coasting to a stop with no lights. With the multiple fuses, a short in one circuit will not always kill the whole bike. This can be a lot safer! But it makes the wiring harness much more complicated.
Probably you have some electrical parts from other bike models, maybe other brands. The switches generally do the same things but the wire colors will be way out of whack if you use a non-Honda switchpod. To use some brands you have to rewire some components: Honda usually switches power to the horn and ignition but others may switch the ground... and when a PO has modified the harness to use a different maker's switchgear all bets are off.
Tackle one circuit at a time. Trace it, referring to the Honda wiring diagram for your model and year from the main fuse right through the harness. Example: the lighting circuits go from the main fuse to the ignition switch, back to the lighting fuses, and then up to the switchpods, finally to the lights.
The lighting ON/OFF switch bypass jumper causes a lot of confusion in particular - if your switchpod has no on/off switch then the brown/black wire at the harness junction under the tank must be jumpered to black. The jumper was a kludge fix for always-on lighting laws, replacement switchpods don't have the jumper and it will easily pull or fall out of the original pod wiring sleeve and can get misplaced.
The OEM ignition switch wiring is pretty strange until you understand it. Using an aftermarket key switch with only a single contact is not a tough job but you have to understand the harness circuits  to maintain the TAIL fuse protection.

[newbhampshire]

Thank you, Bodi and Drlumen, for the help and reenforcement. I just wanted confirmation that I either wasn't losing my mind, or, that I was on the right path. I'll continue to follow the black/yellow, and other stripey lines, til I have it sorted. I'm pretty sure they're stock switches, just too many sources of info at my fingertips makes things a little confusing.  I'll update with the conclusion when I reach one, for posperity.