Topic: ‘77 CB550K3 Running Light Tail Light circuit issues (Brown/White wires)

[damianiscool]

New member really struggling here, just got my first CB, previous owner put on a new wiring harness but didn’t finish wiring everything up. As a result, I’ve done it and learned a ton about this thing, but one thing still evades me.

I have been searching this forum and google up and down to figure out what’s going on, but I just cannot get the Brown to Brown/White circuit to work. Inevitably this means my tach lights, speedo lights, and rear tail running light doesn’t work, but my brake light, instrument lights, headlights and everything else does. The tail light also DOES light up when the keyswitch is set to Park mode.

What I’ve done/tried:
- Just like the wiring diagram, I have the tach, speedo, and turn signal stock Br/W wire hooked up to the Br/W connector coming out of the main wiring harness in the headlight bulb.
- I have confirmed my bulb works on both filaments
- I have confirmed the wiring from under the seat to the tail light is operational
- I am confident the ignition switch is not the problem: I have jumped both the Br wires to the Br/W wire with no difference in behavior and I have swapped my ignition switch with a spare (the prev owner had a bunch of parts), again with no difference in behavior.
- I tried a spare left handlebar stock (with turn signals, horn, and hi-beam switch) and that didn’t fix the problem at all.

So far the only thing that works is to take the Br/W wires out and connect them to one of the Black 12v+ connectors in the headlight bucket or to plug the White wire from the turn signal stock into the Br/W connector in the headlight bucket. But this isn’t really a fix, I don’t think.

I have taken a voltmeter to test voltage but I’m not the best with it. I know I get nearly no voltage (like 90 mV) when testing the female Brown wire under the seat, either side of the tail light fuse, and on the unused Brown wire in the headlight bucket.

Please help, I am sooo confused. This is the last electrical issue I have yet to fix

[scottly]

I have taken a voltmeter to test voltage but I’m not the best with it. I know I get nearly no voltage (like 90 mV) when testing the female Brown wire under the seat, either side of the tail light fuse, and on the unused Brown wire in the headlight bucket.

There should be a brown/blue wire that plugs into a solid black wire, which feeds power to the taillight fuse.

[HondaMan]

The 550K3 has 2 fuses for the lighting circuits: they are both the 7A fuses in the fuseholder. One of them (the Brn wire circuit) gets its power from the keyswitch when ON or in Park position, while the other one gets power on the Bk/Red wire from the unpressed START button to the fuseblock, then from there it goes out as Bn/Red back to power the headlight via the Hi/Lo switch on the left handlebar.

If you wish to get a book that details all these things, keep an eye out for the discounts here:
http://forums.sohc4.net/index.php/topic,65293.0.html
 -this wiring is on page V-10.

Since Honda changed the wiring on the CB550 3 times in 3 years, they can be confusing to work on!

[damianiscool]

There should be a brown/blue wire that plugs into a solid black wire, which feeds power to the taillight fuse.

THIS! This particularly stood out to me because there IS an unused Brown/Blue wire in the headlight bucket, the prev owner took out the turn signal buzzer and just left that wire dangling. Issue is, after trying to hook that Brown/Blue wire up to either of the Black connectirs in the headlight bucket, neither seem to be working to fix the issue. Thank you

[scottly]

So the taillight still isn't working with the brown/blue plugged into a black wire?

[HondaMan]

Yeah, in those bikes with the keyswitch up in the instruments, the keyswitch internally distributes power to the lighting, making the circuitry sort of opaque to follow. Don't overlook the possibility that the fuses are corroded, and their clips in the fuseblock (because it was designed to last 10 years). Also, the fuse type is an SFE: these have not been made worldwide since 1996 when DIN standards took over, and the world ran out of [real] SFE type vibration-rated fuses (old stock) somewhere around 2005. Using appliance-style fuses (ABC/AGC/AGX, etc.) will cause them to break when hitting a bump, because they are not made to support themselves when hot, carrying current: they get soft when hot,and fall apart, making it look like they "blew" for some unknown reason. For that reason, I also make a modern-type fuseblock for these bikes that uses ATC automotive fuses instead. PM me if interested in one.

[bryanj]

I remember there is a "jumper" wire that connects two different colour wires together but i cant remember what to what without a wiring  diagram

[damianiscool]

So the taillight still isn't working with the brown/blue plugged into a black wire?

This is correct, I tested it on both the Black wire connectors that are in my headlight bucket (one from the main harness and the other from the ignition switch). I also tried connecting the Brown/Blue wire to the Brown/Blue wire on the Turn signal buzzer (I still have it, it’s just loose and doesn’t work) and then connected the buzzer’s Black wire to the Black wire connector in the headlight bucket to no avail.

Also, Hondaman, I already have a brand new fuse box, so there’s no corrosion whatsover

[damianiscool]

I remember there is a "jumper" wire that connects two different colour wires together but i cant remember what to what without a wiring  diagram

I would love if this were the solution to my problem (i’ve seen wiring harnesses with that), however after inspecting a listing for my bike’s wring harness, I wasn’t able to fond one with the jumper you’re talking about:
https://ebay.us/m/vwqDbb

EDIT: wait, I found one: https://ebay.us/m/Ij5WyA

[scottly]

Check for 12v on both sides of the taillight fuse again. Place the negative meter lead on the battery negative terminal and use the other meter lead to test with.

[scottly]

In this portion of the K3 schematic, the brown/blue wire from the taillight fuse comes in from the lower right, then connects to a brown/blue jumper with a yellow sleeve on both sides of the connection. The jumper then goes up and loops back down and the end with a black sleeve connects to a black wire right above the other connection.

[damianiscool]

Check for 12v on both sides of the taillight fuse again. Place the negative meter lead on the battery negative terminal and use the other meter lead to test with.

Just finished dinner and came back out. I was able to get 11v on both sides of the tail light fuse. As for the schematic, could you send the entire thing? I’m using the Clymer’s diagram and one I found online but none of them look like that. Thank you again!

[scottly]

Since you have power on both sides of the fuse, the brown/blue wire isn't the problem. The power goes out of the fuse on the brown white wire, so you need to trace it from the fuse towards the left in the schematic.

[scottly]

This may be easier to read?

[damianiscool]

I fixed it! Or at least it appears that way. Thank you sooooo much, Scottly. The diagrams are a bit too blurry, but I didn’t end up needing them. I just used all the info and advice I’ve absorbed over the past day and a half and just tried something and it worked! I have speedo and tach lights and a running tail light!

So here’s what I did (see the magenta-highlighted portions of the photo I attached)
I made my own jumper wire. I attached one end to the Brown/Blue wire coming from the turn signal stock and then connected that join to the Brown/White connector (see magenta circle). The other end I attached to the Black 12v+ connector (see magenta arrow). Also this still has no turn signal buzzer involved.

With that, I think this issue is resolved, that is unless you or anyone sees anything wrong I haven’t noticed. You have the non-blurry diagram, if you could give me your opinion I would be very grateful. Thank you again!

EDIT: yes I will get a bullet connector tool to make this nicer and more permanent

[scottly]

If it works I have no problem with it. After looking more closely at the diagram, it looks like the problem may be with the ignition switch, which connects the brown/white wire from the fuse to the brown taillight wire when the switch is in the On position. In the Park position, the red wire from the main fuse is connected to the taillight brown wire, and the key can be removed. I have no idea why Honda chose to incorporate the Park feature, but that is the only reason the taillight is powered separately from the other lights through the ignition switch...   

[bryanj]

Some countries used to require "parking" lights when left at side of road at night, also why there is a spare brown wire in the bucket at front for a side light, UK calls them position lights and there are a requiremenr

[damianiscool]

I just don’t see how the ignition switch could be the issue after having tested it with my spare, bypassing it entirely by jumping the two wires, and by taking the ignition switch apart. All 3 yielded the exact same behavior of not working.

Regardless, I’m still not out of the woods yet. The rear turn signals don’t blink when I switch them on, they just turn on solid. So I have more work to do. Thanks for the help!

[newday777]

Regardless, I’m still not out of the woods yet. The rear turn signals don’t blink when I switch them on, they just turn on solid. So I have more work to do. Thanks for the help!

If you still have the old thermal flasher, replace it with an electronic flasher. Most of the old flashers exhibit symptoms of that nature now.

[scottly]

I just don’t see how the ignition switch could be the issue after having tested it with my spare, bypassing it entirely by jumping the two wires, and by taking the ignition switch apart. All 3 yielded the exact same behavior of not working.

Regardless, I’m still not out of the woods yet. The rear turn signals don’t blink when I switch them on, they just turn on solid. So I have more work to do. Thanks for the help!

With the key on, there should be 12v going into the switch on the brown/white wire, and 12v coming out of the switch on the brown wire, assuming stock wiring. There was a similar problem a while back, where the problem remained even after replacing the switch, which turned out to be the position of the switch when it was snapped onto the lock, as near as I can recall??
Regarding the turn signals, is your battery fully charged? Before, you only measured 11v at the taillight fuse..

[damianiscool]

Life got busy, but I fixed it!… forreal this time. Finally got a chance to play with it yesterday, just tried something and it worked!

Here’s what I did:
It made little sense to me to wire 5 wires into the Brown/White connector that only has 4 wire slots, so I said screw the Brown/Blue turn signal wire. Instead I tried just taking my jumper wire and connecting it from the black 12v+ to the unused Brown (Brown/Black in my case) female connector in the headlight bucket. To my surprise, that worked! My speedo, tach, and running light all work and my back blinkers blink too! I attached a photo

Thanks everyone for their help! Every single electrical issue has been fixed now!