Topic: No instrument lights, blowing fuse

[joegeis]

I've been gleefully riding my CB550 during the daytime with no issues. Everything seems to be working. I ended up out at night the other day and I realized the speedo and tach have no lights! I tested the bulbs and they all still work fine. I checked for power in the brown connector bundle in the headlight bucket, and no power there either. I checked my fuse block and I had a blown fuse. I replaced it and it immediately blew again. I have Hondaman's blade fuse block upgrade installed, so I don't have anything labeled there, but it is the brown and white wire. I was getting a ground fault. The brown connector housing on my headlight bucket has the supply, one br/wh wire per instrument, and a third br/wh that goes to the left switch housing. That wire is what was causing the ground fault. I have it disconnected now and everything is fine, so I'm confused as to what its purpose is. The only thing I can think of is that I removed the turn signal buzzer. Was the only purpose of this wire to power that? If so, I guess I am all done here and have no need to try and "fix" this grounding (maybe its the br/blue wire grounding out in the bucket?).

Or am I missing something thats not so obvious?

[Deltarider]

You didn't specify your model. Consult the appropiate wiring diagram only.

[denward17]

I think he is referring to his 1978 550K model.

[joegeis]

sorry, yes, this is my 78 CB550K. It does not have an on/off switch for the headlight. Headlight is always on.

[Don R]

https://oldmanhonda.com/MC/WiringDiagrams/CB550.jpg
 
 There really aren't any extra wires. I'd suspect something else isn't working and may be grounded. Did the beeper work before?

[HondaMan]

Maybe try this test: unscrew the 2 handlebar switches and let them lay open, then test it again (with another fuse? You can get the ATC fuses everywhere, even the grocery store has them). It's not uncommon for the 50-year-old vinyl jackets on the wires at the switches to crack now. The middle fuse (black wires at the fuseblock) is the taillight circuit if the loom is still originally configured, with the top (brown wires) being the tail and instrument lights. In my book, Section V Page 10 shows the lighting circuits and fuses for your version of the bike.

[joegeis]

I marked up the wiring diagram to explain what I'm seeing. My bike does not have a headlight switch. The brown wire I marked red doesn't exist for me. The brown wire I highlighted yellow is the one I have unplugged to prevent the ground and blowing the fuse. Everything on that switch housing still works - high beams, turn signals, horn. I removed the signal buzzer two years ago, and it was working when it was removed.

[scottly]

I marked up the wiring diagram to explain what I'm seeing. My bike does not have a headlight switch. The brown wire I marked red doesn't exist for me. The brown wire I highlighted yellow is the one I have unplugged to prevent the ground and blowing the fuse. Everything on that switch housing still works - high beams, turn signals, horn. I removed the signal buzzer two years ago, and it was working when it was removed.

The wire marked in yellow is for the taillight. There may be a short to ground in the wiring to the taillight; a common place this can happen is where the taillight wiring passes through the rear fender. There is supposed to be a rubber grommet in the hole to protect the wiring. Another place might be inside the taillight housing under the red lens. Also, the taillight fuse should be 5 amps.

[HondaMan]

For the 1977/78 CB550K/F bikes, for some reason Honda switched to 7 Amps for the taillight fuse circuit. Nothing else changed but the fuse(?) from the earlier bikes, though.

[Deltarider]

I marked up the wiring diagram to explain what I'm seeing.

I would not call that the appropiate wiring diagram.

[joegeis]

I also used the one in the back of the Clymer (though I still need to reference Mark's book, which is sitting right next to the Clymer!)

I did confirm my tail light is still working, even with that wire headed to the switch disconnected. This is a mystery wrapped in an enigma. I'll check Mark's book and diagram when I get home.