Topic: 1975 CB400f left hand controls and horn wiring issue

[kfleschner]

Hello! I've got a bit of an question I'm hoping someone can help clear up. I've got a 1975 CB400f. I just moved to NY and was told at inspection that the horn needs to be functional to be legal. The left hand control has a missing horn button. So one new reproduction left hand control order later (This one - http://4into1.com/reproduction-left-switch-assembly-35200-377-003-honda-cb360t-cb400f/) and I've got a switch assembly that fits, but the wires don't match up to the bike's wire harness. The broke control has wires for a clutch switch feeding into the headlight bucket that the new one doesn't have. The old control has O/W and B/W wires that match the wire harness. The new one doesn't have those two, but has an additional black wire. The whole point of this was to get the horn functional again, but now I've got a black wire doing who's knows what from the new control and a horn black wire that's got a bullet connection on it with no where to go. Is there a way to get this wired properly, or do I need to go back and get a different left hand control?

[Bodi]

You need to meter the switchpod connections to figure out what wire is controlled by the horn button. The original horn wiring has the horn powered all the time and the button connects ground... your new one may switch power to the horn and you might need to ground one horn terminal?
It seems like this is not an exact replacement. I think DSS sells exact ones... but probably make what you have work.
The O/W and B/W wires are for the turn signal function... the front marker lights power from these I think, the original switch cuts the signaling side's marker off.The grey harness wire is from the flasher, this should be switched to the respective side's signal wire (orange=left and blue=right).
I don't know what color code this pod uses... Honda black is always switched (key ON) power on SOHC4 bikes. But black is not present in the stock switchpod.
Basically... measure resistance from each wire to all the others, switch each switch while measuring and note the differences in a complicated chart. There aren't all that many functions - headlight hi/lo, signals, and horn. Even if the horn button does expect to switch power (presumably from the black wire?), if there aren't any other switch functions that use the black wire power you can just connect the pod's black to ground and the horn wire to the harness light green (horn switched ground) wire.
Download a Honda service manual wiring diagram for the 400F. Don't go by a Clymer, Haynes, or whatever wiring diagram.... they are all slightly wrong is oddball ways.

[Deltarider]

Download a Honda service manual wiring diagram for the 400F.

I don't know about the CB400F but the CB500/550s had different horn wiring schemes for various markets and so the CB500 Owner's Manual contains no less than 4 different schemes for various markets. You may also consult the Part List to check, by observing the area codes, which model switch assy is supposed to be on yours. http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb400
If you ordered (or received) the wrong model, I'd return it.

[kfleschner]

How about the wiring diagram from the shop manual? Is that one reliable?

[Deltarider]

How about the wiring diagram from the shop manual? Is that one reliable?

Unfortunately it doesn't specify what model (area code) it covers. In the last pages ot the CB400F Owner's Manual http://www.honda4fun.com/pdf_libretti/400/Libretto400_5.pdf you'll find four different wiring diagrams. Maybe it can be of some help.

[calj737]

How about the wiring diagram from the shop manual? Is that one reliable?

You really just need to exchange the part for the model correct unit, or, follow Bodi's advice and identify each button/wire from your control with a meter. Meters never lie when used correctly. Much faster and easier than sifting through diagrams, and a litany of models.

[Bodi]

Yes there are several slightly different wiring diagrams for different countries/areas. The linked booklet pdf has four (pretty much unreadably low resolution) wiring diagrams - all are European areas though ... no US/Canada version. I haven't found a downloadable diagram that shows the front marker off-when-signaling connections, but the diagram in my hard copy original service manual (bought from a Canadian Honda dealer way back when) does (I think).

[magnum56]

See if one of the "interactive" wiring diagrams located at the link below can assist you.

Allows you to enable and disable areas of the wiring diagram related to the functions you are most interested in.

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

[Deltarider]

... no US/Canada version. I haven't found a downloadable diagram that shows the front marker off-when-signaling connections

Yoe mean like this one:
http://manuals.sohc4.net/cb400/technical_reference/WD40077.jpg

[kfleschner]

Here's the resolution of the control wiring and horn. I'm sure most of this will be 'well, duh' to most people on here, but just in case someone like me happens to search , here's how I logic'd through it.  ;DStarting with what I know, as stated above:
1) The wiring harness was of the US type based on the presence of o/w and lb/w wires.
2) The left hand control was based on the UK wiring harness. This has an additional black wire, and absence of the o/w and lb/o wires.

So referring to the UK wiring diagram found on the forums, the black wire goes to the frame. In the US diagram the black wire goes to the black in the wire harness. Easy enough to fix. I just screwed the bullet connector of the horn's black wire into a post connector and put that on the coil mounting bracket as that was nearby. 

Matching up the rest of the wires from the control to the harness left the lb/o and o/w end on the harness open. So back to the US wiring diagram and shop manual. The left hand control switch o/w and lb/w wires are connected to the PR and PL posts. Those wires connect the switch to the front turn signals, indicated to have three wires. My aftermarket turn signals don't have those, so loss of input doesn't matter. The UK wiring diagram lists those wires as empty anyways.

Hooking everything up and everything seems to work fine for now.

[calj737]

The BLACK from stock harness on your horn was switched power. If you connect the LT Green from HORN in the harness to your new LH control, what wire does that go to now? It better be powered... or, you need to reverse the horn BLACK to LH power and LT Green in the harness to ground.

In the stock harness, all BLACK wires are powered. Just in case you didn't realize that-

[przjohn]

I had the same issue when I did a 400F resto a few years back. Problem is I can't remember what I had for breakfast never mind what wire goes where. I give alot of credit to the guys here who can, off the top of their head, tell you wire colors and placement. You may have like I did, the European version that uses a passing switch. I did just as Bodi suggested, Ohming out, tracing, and making the necessary adjustments to the wiring. I don't think you will find any diagram to combo the US and European harness and control. Not that difficult if you have some basic electrical knowledge. If you get really stuck I could pull my headlight this weekend and send you some pics.

[kfleschner]

Yeah, the black wire on the horn kept tossing me for a loop too. The new control has a black wire of its own that powers the horn and the 'passing switch'. It goes in to the harness where the horn's black wire used to go. With the switch in the 'horn' position, pressing the horn button bridges the black to the LG wire feeding the horn. In the passing position it bridges to the high beam, so I guess its intended to flash high beams at people when you pass or something. Short story is the the switch turns the LG wire into the black wire, and the horn's black wire then becomes the ground. I can think of less confusing ways to do it, but everything seems to be working.

[calj737]

Perfect.

[Bodi]

Just test that flashing hi beam when hi beam is already on (if that's possible) doesn't blow a fuse...