Author Topic: 1976 CB550K wiring harness question (Read 4870 times)

fatmatt650 · « **on:** March 12, 2018, 12:24:11 PM »

I was just gifted a 76 550K. P.O. hacked up the wiring harness and apparently grounded something as a good chunk of it in the fuse box neighborhood is completely burnt.
I'd like to replace the entire harness but cannot find the correct one (Honda part # - 32100-374-700)
Mooshie has a 76 F model and tells me the F and K harnesses are cross compatible. Can anyone else verify this before I go buy one? Thanks.

TwoTired · « **Reply #1 on:** March 12, 2018, 01:08:29 PM »

Probably hooked up the battery backwards. That lets out the magic smoke.

Unfortunately, the 76 CB550 K model has a unique harness. Earlier models had that Starter safety module and associated wiring. The 76 K has the simple diode like other later bikes.

The F models have the keyswitch up between the dials, rather than under the left side of the tank. Further, they have a junction area for bar controls and cover under the left side of the tank. The K models don't have that for year 76. So wire lengths and termination points are way different.

77 550K have block connectors for the bar controls that the earlier models don't have.

I think you are looking at robbing a used one, year/model specific, or repairing the one you have using bits from other harnesses.

Cheers,

fatmatt650 · « **Reply #2 on:** March 12, 2018, 03:54:39 PM »

Thanks for the info. I've got a couple other wiring harnesses laying around. Maybe I can Frankenstein something together.

ts354 · « **Reply #3 on:** March 12, 2018, 06:22:18 PM »

FatMatt650/Two Tiered- I've got the same problem. I have looked at the '74K-'75K wiring harness and it is very close to the '76K.
- '74-'75K's have 6 wires out of the right hand controls and 10 out of the left hand control. (not counting brake or clutch switches)
- '76K has 5 out of the right hand controls and 11 out of the left. (not counting brake or clutch switches).

- '74-'75K's have 5 wires going to the starter motor safety switch.
- '76K has only has 2 going to a diode.

Everything else looks the same. I may just buy a 74-75 starter motor safety switch and put that on my bike instead of the diode. My left and right controls are shot anyway. I will just buy cheap after market replacements for the 74-75 model and then I should have a '76K bike wired just like a 74-75.

fatmatt650 · « **Reply #4 on:** March 12, 2018, 07:12:39 PM »

I'd love to see how that works out for you. I'm hoping the couple used harnesses I have laying around have enough similarity that I can use them to fix mine. P.O. cut it at a few places when he ditched the signals and clocks but the worst part is the fused mess of plastic and copper around the solenoid/fuse box area. Not sure if I'll have compatible plugs.

scottly · « **Reply #5 on:** March 12, 2018, 07:30:54 PM »

Quote from: ts354 on March 12, 2018, 06:22:18 PM

- '74-'75K's have 5 wires going to the starter motor safety switch.
- '76K has only has 2 going to a diode.

Everything else looks the same. I may just buy a 74-75 starter motor safety switch and put that on my bike instead of the diode.

You can fit the diode in place of the SMSU, using only two of the early harness wires, but you can't fit an SMSU in place of the diode on the later harness, as you are missing three wires. The diode is the better option anyway..

fatmatt650 · « **Reply #6 on:** March 13, 2018, 04:12:28 PM »

A photo of the offending wire.

fatmatt650 · « **Reply #7 on:** March 13, 2018, 06:49:10 PM »

Green (toasted) wire is showing positive current when battery is connected. That's bad, right?

Also found a similar condition of meltiness in the headlight bucket where the right hand green ground wire attaches to the headlight bucket ear.

scottly · « **Reply #8 on:** March 13, 2018, 07:01:53 PM »

Matt, just for grins measure from the frame to the battery - terminal.

fatmatt650 · « **Reply #9 on:** March 13, 2018, 07:03:50 PM »

Quote from: scottly on March 13, 2018, 07:01:53 PM

Matt, just for grins measure from the frame to the battery - terminal.

0.00

scottly · « **Reply #10 on:** March 13, 2018, 07:13:07 PM »

The rectifier is likely shorted, and was probably caused by reversing the battery polarity, as Lloyd said. You may be able to repair the harness, but you will have to unwrap it to make sure the insulation wasn't melted through on the other wires in the harness.

fatmatt650 · « **Reply #11 on:** March 13, 2018, 07:16:50 PM »

Quote from: scottly on March 13, 2018, 07:13:07 PM

The rectifier is likely shorted, and was probably caused by reversing the battery polarity, as Lloyd said. You may be able to repair the harness, but you will have to unwrap it to make sure the insulation wasn't melted through on the other wires in the harness.

I'll see if I can figure out a diagnostic for that, thanks. I did just notice I'm reading 12.5 volts at all three connections to the regulator. That seems odd.

scottly · « **Reply #12 on:** March 13, 2018, 07:22:45 PM »

Is that with the key on?

fatmatt650 · « **Reply #13 on:** March 13, 2018, 07:29:53 PM »

Yes. I pulled the green wire from the rectifier and it now no longer reads positive charge at the various green wires. Brake, oil and neutral lights all work now. Still a very mild blue spark when I connect the battery terminals but not as bad as it was. Here's the weird one - I pulled a spark plug to check for spark (crossing the solenoid terminals as the starter switch is not functioning), no spark, the turn signals have been removed but I flicked the switch anyway and when I did the spark plug sparked.

fatmatt650 · « **Reply #14 on:** March 13, 2018, 07:36:50 PM »

P.O. had connected the gray and black wires at the turn signal directly to each other, when I saw this I disconnected them. After seeing the weird spark issue, I reconnected them and it now has good spark.

scottly · « **Reply #15 on:** March 13, 2018, 07:40:17 PM »

Do you still get a spark when connecting the battery? If the key is off when connecting, it's a problem. If the key is on, it's normal.

fatmatt650 · « **Reply #16 on:** March 13, 2018, 07:50:55 PM »

Quote from: scottly on March 13, 2018, 07:40:17 PM

Do you still get a spark when connecting the battery? If the key is off when connecting, it's a problem. If the key is on, it's normal.

Looks like all is normal then, thanks. Just shot some brake cleaner in one of the carbs (pod filters) and that cylinder started firing after just a couple kicks. Woohoo! Looks like I just need to get a new reg/rec and do some housekeeping on that wiring harness.

/and then figure out what back DMV fees till 2011 are gonna be $:-\$

fatmatt650 · « **Reply #17 on:** March 13, 2018, 07:52:11 PM »

The "free" bike in question -

scottly · « **Reply #18 on:** March 13, 2018, 07:56:25 PM »

Get that fuggen ugly exhaust wrap off, and it might look half decent.

TwoTired · « **Reply #19 on:** March 13, 2018, 08:15:03 PM »

When I got my 76 CB550F, that green wire was toasted like yours from that connector all the way up the frame spine to the ring-terminal-to-frame at the coil mount.
I unwrapped the harness and replaced all the crispy insulated wires in the harness that got damaged during the burn. I had a spare Harness from a 77 that had all the wire colors I needed. I spliced in the replacement wires in place of the melted sections (soldered and shrink wrapped). Then taped the harness back up. In my case, the reg and rectifier was still good. So, I'm pretty sure the battery was wired in backwards somehow before the junkyard acquired it my subsequent purchase from them. Anyway, it's been fine since the repair. Time consuming, for sure. I think I spent a nice summer day in the garage shade doing the repair.
I have fun fixing things that others toss aside.

Cheers,

fatmatt650 · « **Reply #20 on:** March 13, 2018, 08:19:45 PM »

Quote from: TwoTired on March 13, 2018, 08:15:03 PM

When I got my 76 CB550F, that green wire was toasted like yours from that connector all the way up the frame spine to the ring-terminal-to-frame at the coil mount.
I unwrapped the harness and replaced all the crispy insulated wires in the harness that got damaged during the burn. I had a spare Harness from a 77 that had all the wire colors I needed. I spliced in the replacement wires in place of the melted sections (soldered and shrink wrapped). Then taped the harness back up. In my case, the reg and rectifier was still good. So, I'm pretty sure the battery was wired in backwards somehow before the junkyard acquired it my subsequent purchase from them. Anyway, it's been fine since the repair. Time consuming, for sure. I think I spent a nice summer day in the garage shade doing the repair.
I have fun fixing things that others toss aside.

The thing I love the most about working on the spaghetti system is when it's over.
But seriously, it's very satisfying to bring something back to life that was otherwise destined for the scrapyard. Thanks again for all the excellent advice.
Cheers,

fatmatt650 · « **Reply #21 on:** March 13, 2018, 08:21:51 PM »

Quote from: scottly on March 13, 2018, 07:56:25 PM

Get that fuggen ugly exhaust wrap off, and it might look half decent.

But that's what makes it a "cafe racer"!
I actually am interested to see what's under there. Judging by the rest of the bike, probably a nice shiny set of pipes. Now I need to find a muffler with some baffles in it.

scottly · « **Reply #22 on:** March 13, 2018, 08:31:32 PM »

Quote from: fatmatt650 on March 13, 2018, 08:21:51 PM

Quote from: scottly on March 13, 2018, 07:56:25 PM
Get that fuggen ugly exhaust wrap off, and it might look half decent.

But that's what makes it a "cafe racer"!

Exhaust wrap makes it a "hipster racer".

amitr0 · « **Reply #23 on:** December 30, 2021, 01:21:24 PM »

Quote from: scottly on March 12, 2018, 07:30:54 PM

Quote from: ts354 on March 12, 2018, 06:22:18 PM

- '74-'75K's have 5 wires going to the starter motor safety switch.
- '76K has only has 2 going to a diode.

Everything else looks the same. I may just buy a 74-75 starter motor safety switch and put that on my bike instead of the diode.
You can fit the diode in place of the SMSU, using only two of the early harness wires, but you can't fit an SMSU in place of the diode on the later harness, as you are missing three wires. The diode is the better option anyway..

I have the same problem. Can you explain a bit why the diode is a better option than the relay/switch?

amitr0 · « **Reply #24 on:** December 30, 2021, 01:26:14 PM »

Quote from: ts354 on March 12, 2018, 06:22:18 PM

FatMatt650/Two Tiered- I've got the same problem. I have looked at the '74K-'75K wiring harness and it is very close to the '76K.
- '74-'75K's have 6 wires out of the right hand controls and 10 out of the left hand control. (not counting brake or clutch switches)
- '76K has 5 out of the right hand controls and 11 out of the left. (not counting brake or clutch switches).

- '74-'75K's have 5 wires going to the starter motor safety switch.
- '76K has only has 2 going to a diode.

Everything else looks the same. I may just buy a 74-75 starter motor safety switch and put that on my bike instead of the diode. My left and right controls are shot anyway. I will just buy cheap after market replacements for the 74-75 model and then I should have a '76K bike wired just like a 74-75.

What specifically was drooped from the right and added to the left? What did you do two these missing/relocated wires?

News:

Author Topic: 1976 CB550K wiring harness question (Read 4870 times)