Author Topic: 78 cb750 wiring help on NH seacoast (Read 7676 times)

sethmcalister · « **on:** July 04, 2014, 01:23:19 PM »

Is there anybody near the Portsmouth, NH area that could give me a hand re-wiring my 78 cb750? I'll supply the beer.

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calj737 · « **Reply #1 on:** July 04, 2014, 02:03:00 PM »

Quote from: sethmcalister on July 04, 2014, 01:23:19 PM

Is there anybody near the Portsmouth, NH are that could give me a hand ~~writing~~ wiring?

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FTFY. Unless you meant spelling?

Seriously, though. Anything we can help with remotely, Seth?

sethmcalister · « **Reply #2 on:** July 04, 2014, 02:27:54 PM »

Damn autocorrect. Thx! I'm not sure where to start, to be honest. My bike had an old windjammer fairing on the front. Whomever installed it definitely made the wiring their own. I started re wiring and it was extremely messy so picked up a new harness from vintagecb750.com. But, it still wasn't quite plug and play.

My blinkers are working (led), my brake light works, but nothing else seems to work.

Some of the wires still had to be spliced, like the headlight plug. I have the wiring schematics, but wiring is definitely not my thing.

I don't know where to start though really.

I know that I have an orange/white and light blue/white coming from the left control that don't plug in to anything, but I don't see those colors on the schematics.

I don't know why the brake light works, but the taillight isn't. No horn. No headlight. No neutral light.

The front stop switch is hooked in but I don't know where it mounts and it actually looks like it's kind of broken.

You let Mr know what you need, description/pictures and I'll give em to ya.

Thx Cal

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calj737 · « **Reply #3 on:** July 04, 2014, 05:31:46 PM »

Are all the components stock? This is something that can be solved, taken section by section.

sethmcalister · « **Reply #4 on:** July 05, 2014, 12:09:48 PM »

The blinkers are not, but those are working. The headlight is an H4 from DCC. The horn came from vintagecb750. Everything else is stock.

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madmtnmotors · « **Reply #5 on:** July 05, 2014, 04:25:57 PM »

Quote from: sethmcalister on July 04, 2014, 02:27:54 PM

picked up a new harness from vintagecb750.com. But, it still wasn't quite plug and play.

Some of the wires still had to be spliced, like the headlight plug.

Not sure why the headlight plug would have to be "spliced" into a replacement harness, unless the headlight plug did not have connectors?

From what I understand there are a couple of peculiarities to the aftermarket harnesses. Here are a couple detailed write ups:

http://forums.sohc4.net/index.php?topic=110411.0

http://forums.sohc4.net/index.php?topic=110284.0

sethmcalister · « **Reply #6 on:** July 05, 2014, 05:25:01 PM »

The headlight plug was taken off the headlight from the fairing but it needed to be cut so I needed to splice it into the new harness. I had found a couple write ups about peculiarities, but do you think I could find them again? I'll read over what you've posted now.

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sethmcalister · « **Reply #7 on:** July 06, 2014, 12:59:29 PM »

Alright. Made some progress. One of my fuses was blown so picked up a new one. Following the post links from MadMtn resulted in my jumping the single leftover brown in the headlight bucket into one of the black four way connectors (there was no single black). My taillight works now, however, now when I flip a blinker it just stays on and doesn't blink.

In one of the links above it talks about two brown/red wires but I only have one. I know my headlight isn't working because the low beam isn't tied into the main harness so I'll need to fix that, but I'm not sure how to do it yet. Horn still doesn't work. Neutral light doesn't work. High beam indicator in the dash works when the plug isn't hooked into the headlight.

What do you guys think?

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calj737 · « **Reply #8 on:** July 06, 2014, 01:16:05 PM »

Neutral light wire is green/red wire coming from under left side cover, found in the loom. Sounds like your flasher is wonky re:turn signals not working.

madmtnmotors · « **Reply #9 on:** July 06, 2014, 01:48:19 PM »

So the blinkers used to flash and now they just come on and stay on?

Check the bulb in the dash for the neutral light first, make sure it's not blown.

sethmcalister · « **Reply #10 on:** July 07, 2014, 03:43:27 AM »

The blinkers worked perfectly before jumping the brown wire in the headlight into a black four way. Now, when i hit left the left side comes on and stays on and the same for the right side. Im going to pull the jumped cable out to see if that is the problem.

I'll check the neutral wire/indicator light when I get home today.

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sethmcalister · « **Reply #11 on:** July 08, 2014, 05:46:01 AM »

I made a little progress last night. Taillight and headlight are working. If I push the blinkers all the way, they stay on, however, if I hold it just before it clicks in they flash.

The starter, horn and neutral light still aren't working. The starter solenoid works and the black wire in the wiring harness in the headlight has power. Not sure what else I should look for here?

madmtnmotors · « **Reply #12 on:** July 08, 2014, 06:11:35 AM »

Have you verified that the bulb for the neutral light is a good working bulb?

Electrical diagnosis and repair requires a methodical, step by step process of elimination. I often find electrical diagnosis requires finding out what it's not.

sethmcalister · « **Reply #13 on:** July 08, 2014, 06:12:56 AM »

Yes, I've verified that a working bulb does not work in the neutral light. Looking at the wiring schematics, the neutral light, horn and starter button are all tied together which would indicate there's some issue keeping all three from working. Would that make sense in thinking that?

calj737 · « **Reply #14 on:** July 08, 2014, 10:23:47 AM »

Seth - the green/red wire for your Neutral light comes from under the left side cover. The black, is a shared wire to horn switch and the start button. But the black on the horn switch is a ground interrupt for the horns to sound.

The black wire for the start switch is 12v switched power, coming from the start/stop switch (as I look at your year's diagram). Not sure how your bike is wired,it I'd encourage you to test continuity from the horn "black" to the start button "black" to determine if they're somehow tied together on your bike after the PO mods.

sethmcalister · « **Reply #15 on:** July 08, 2014, 10:32:01 AM »

I've replaced the harness with a new one so all of the connections should be stock now. The horn is new (from vintagecb750). Is it possible that the diode is no good?

Also, I can't figure out how my front stop switch is supposed to mount. I know it belongs on underneath the master cylinder but how? I can't seem to see how the brake lever actuates the switch?

calj737 · « **Reply #16 on:** July 08, 2014, 10:38:42 AM »

For the turn lights, I'd suspect the winker relay is bad.

Regarding you're front brake switch, on my bike (74 550) it's a 3-way that uses a pressure switch to activate the front brake. On other models that use a switch mounted to the lever/perch, they are wired to ground and to the harness circuit that "powers/signals" the actual brake light. Got a picture or two of your config. I don't have a 750 manual to look at...

sethmcalister · « **Reply #17 on:** July 08, 2014, 10:43:48 AM »

The winker relay is brand new and was working until I jumped the brown wire for the taillight into the black per MadMtn's posts from earlier. They work, but not if I click them all the way over.

I've been trying to find a picture of how it's setup and I haven't had any luck aside from the schematic from csmnl.com.

calj737 · « **Reply #18 on:** July 08, 2014, 10:56:25 AM »

The brown for the tailight should be connected to the brown at the ignition switch. The brown from the headlight is an extra wire.

I'd be confused/concerned as to the headlight bucket brown connecting into the blacks. Those are either switched 12v wires or grounds. The brown should not be part of either of those circuits that I can see.

sethmcalister · « **Reply #19 on:** July 08, 2014, 11:00:50 AM »

This was due according to this post from Hondaman:

http://forums.sohc4.net/index.php?topic=110284.0

madmtnmotors · « **Reply #20 on:** July 08, 2014, 02:08:49 PM »

Quote from: calj737 on July 08, 2014, 10:38:42 AM

For the turn lights, I'd suspect the winker relay is bad.

This may be partially true. You indicate that you have LED turn signals. There are numerous posts about getting a "proper" turn signal relay to work with LED lights. The LED lights often do not generate enough resistance to "activate" the stock turn signal relay. This could partially explain your inconsistent results with the turn signals.

sethmcalister · « **Reply #21 on:** July 08, 2014, 02:17:00 PM »

Correct, but I have an LED compatible electronic relay and resistors set up which,as far as I've read, is sufficient for these to work properly.

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calj737 · « **Reply #22 on:** July 08, 2014, 02:20:28 PM »

Except, you've jumpered the brown wire into the black and might be bypassing the relay to send the signal. You need to test this with a meter from the turn switch, to the relay. Make sure your power and resistance is consistent to illuminate the indicator.

And, have you refurbished the actual bar control switch?

sethmcalister · « **Reply #23 on:** July 08, 2014, 02:28:20 PM »

This is where my lack of wiring knowledge comes in...how do I test that?

The controls have not been refurbished, as far as I know. The starter worked with the old harness though.

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madmtnmotors · « **Reply #24 on:** July 08, 2014, 07:37:27 PM »

You will have to trace your problem circuits out one by one, systematically, until you find the problem(s). That's the nature of the beast with electrical troubleshooting. If you try to focus on or solve too many issues at once it's difficult to track your progress, or to determine if you've inadvertently introduced other problems. Fix one issue and move to the next. Using the aftermarket harness has introduced variables that cannot be solved by simply following the factory wiring diagram. The factory diagram now becomes a guide to determine the differences between your harness and the factory harness. One problem circuit at a time, using a multimeter (volts/ohms) to check for either continuity or voltage, whichever is appropriate for the section of wire you are testing, depending on whether you expect it to be energized or simply continuous (or connectivity as in checking the operation of a switch).

I see four options:

>Find an OEM harness
>Seek professional help (a lot of hacks out there though). This could also be expensive due to the non stock harness.
>Ply a friend/colleague (that can read a wiring diagram and use a multimeter) full of beer and steak to get them to help.
>Learn to read a wiring diagram and to use a multimeter.

There's no easy way out with electrical troubleshooting, especially with the variables introduced by the aftermarket harness. Patience and a process of elimination are the only way. Here is an interactive wiring diagram to get you started on your way to mastering the electrical system (and wiring diagram) of a CB750:

http://oldmanhonda.com/MC/wiring750K1.html

Now this is for a 1971 750 which is different (but very similar to) the 78' but should help you understand the basics of reading a wiring diagram.

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Author Topic: 78 cb750 wiring help on NH seacoast (Read 7676 times)