Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: royhall on May 11, 2023, 11:39:41 AM
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Good morning all. This is for you budding auto electricians out there. The 750 has arrived at the wiring stage. Starting at the back and working forwards all has gone okay including non standard reg/rect and Boyer ignition. Just got to sort out the pan of spaghetti in the headlight. That's brought up the first issue. Why are there 3 cables shown on the front indicators and only 2 on the rear. The actual units just have supply and earth. I am sure I have done this loads of time before but it has me stumped this time. Cheers.
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Is it for US style orange front marker lights?
Running light/sidelights do they call them.
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Is it for US style orange front marker lights?
Running light/sidelights do they call them.
Beat me to it Ted, only needed at the front.
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Daft thing is I only thought it was for orange marker lamps as my Boss in the car trade back in 1971 had a Ford Gran Torino - with the orange fire stripes down the side.(Remember Starsky & Hutch).
Might be wrong though?
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Thanks chaps. I assume then that the blue/white cable can be ignored as the UK spec front indicators have no provision for that.
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You can use them to run a buzzer if you like. As they did in the 70s
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You can use them to run a buzzer if you like. As they did in the 70s
Eeeerrr no thanks.
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Paint the bike gold and black, get the buzzer going and pretend to be a bloody big wasp, what's not to like??????? :D :D :D
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Actually joking aside, I have too many blue wires in the headlamp. But as it's a USA bike there will be one for a buzzer. Nice one.
EDIT. Scratch that the buzzer wire is brown.
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Dark blue or light blue?
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Light blue. I'm just in the process of belling them all through at the moment. Pain of a job so may take a while.
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Mine is a UK bike (K6). It has buzzers on the indicators. Goes for the duration on left turns, only once, then off on right.
I had thought it was a US only thing?
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No UK bikes got them for a couple of years, my 550F2 has one. They were removed after concerns blind people could confuse them for the sound for the safe to cross signal for pedestrian crossing.
That's a really complicated left hand switch there Roy, first time I've seen a really good diagram of one laid out like that. It looks as though they used the Orange/White and Light Blue/White wires to run running lights through the indicators whereas we used them to run the buzzers BUT what's interesting is that the lights go out when the indicators are used to avoid any confusion, so using the left would mean the running light filament in the left bulb goes out whilst the indicator filament flashes but they right hand one stays lit. What a weird setup.
Plus why use a brown wire when there is already a brown wire in the headlight used for power to the headlights?
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To be honest the whole lot is confusing. At the moment I am belling everything through one at a time and labelling them. This is going to be a long job so I think I will spread it over a few days. And this thread is only the first question.
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Mine is a UK bike (K6). It has buzzers on the indicators. Goes for the duration on left turns, only once, then off on right.
I had thought it was a US only thing?
No buzzer on our UK K6 🤔🤔🤔🤔
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Here's an example. The output from the flasher relay unit is grey on the diagram, on mine it is light blue with a darker blue fleck but comes out of the harness at the headlight end as grey. WHAT!!!
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Yep Roy that's why I hate electrics with a passion. :( :( :(
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But wouldn't the connections for the flasher relay be on the sub loom Roy? In which case the sub loom isn't standard. They are always grey on Hondas for some reason. Sometimes a 3 pin relay and sometimes a 2 pin with no earth connection.
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No sub loom on a 750 Ken. Its just three wires bundled out of the main loom. The new loom has light blue, black, & green (unused due to two connection relay). The original harness has the same except light blue is grey. Why it exits the other end as grey heaven only knows, must be connected to something mid loom.
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No sub loom, never spotted that, but then I avoided working on the 750 whenever possible, didn't like it then, still don't like it. Personal choice, just hated that 1st gear clunk sound, made me wince everytime I heard it.
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The only sub looms on a 750 are to the idiot lights and from the alternator.
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Mine is a UK bike (K6). It has buzzers on the indicators. Goes for the duration on left turns, only once, then off on right.
I had thought it was a US only thing?
No buzzer on our UK K6 🤔🤔🤔🤔
Yep, that's what I expected. Odd. Definitely, 1st registered in UK. It's a late K6, not registered until 1977.
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Am nearly there with the wiring, the stuff in the headlight is an awful mess but once I get the connections right I will tidy it up and remove the bulk where required one cable at a time. My next question is, on a K5 (being a USA only model) does the headlight stay on dipped beam whenever the ignition is on. The back light operates okay on and off with the right handlebar switch but the headlight stays on whatever. It does correctly switch to high beam with the left handlebar switch though. Is this correct. Cheers.
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If its lights on wiring the rear light should be on as well. Also when you press the starter the headlamp should go off.
I do not know when, or with which model the change occured but i do know that both aftermarket looms and switches cause havok with different wire colours to Honda.
Long distance wiring problems are a real bitch to sort out but if you have a multimeter and can follow instructions i will try and help you out.
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Thanks Bryan. It's getting a live from somewhere to the dipped beam and I cannot figure out where. Your right about the wrong wire colours I have spent the last 2 days belling everything through. All appears okay except for the headlight. Am just going out now so will resume the hunt tomorrow if your online.
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I am away for a week from tomorrow, may be able to read andreplt, depends on black holes, as i said i will try and help but we need to start from scratch mate
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Already spent 2 days belling every wire through and labelling them. Everything is right except for the low beam issue (white wire from dip switch) appears to be picking up a live from somewhere. I will find it eventually.
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As it is a late USA model, are the running lights not in the indicators Roy ?
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The wiring diagram on post 1 makes no sense. Headlight switch, why a neutral? it's either high or low as a rule plus the connection diagram is wrong, brown would connect to white when on low, not white to blue and in neutral it seems that both high and low are lit? is neutral side lights? if so surely they'd be on the right hand switch?
Check the wires coming out of that switch Roy, when it's on low check which wire has 12v besides the brown, that's the low beam wire. Make sure that's the one going to the bulb as it sounds like you've plugged the wrong one in.
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I think it's more complicated than that, I just discovered the headlight is not running through the fuse box. The big problem yet again is garbage pattern parts, both the loom and the switches contain wrong colour cables. Surely if your going to all the trouble of replicating these things you would use the right colour cables. How hard could that be. Maybe it's to stop Honda issuing legal proceedings for stealing their designs. Makes a simple job bloody difficult. Your right Ken, on low according to the diagram there would be no headlight at all. Am going to start again on the lights.
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How the hell have they managed that Roy? the brown wire comes from it's own fuse in the 3 fuse fusebox, surely they'd have copied the original wiring? even if the colours are different they'd need the wires to go to the right place. Where's this new loom come from?
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I think the looms are made in Vietnam, I have had them before and they were spot on. An example is the flasher relay, goes into the loom from the flasher as light blue (wrong) and appears again in the headlamp as grey (correct). Works okay though after a bit of multimeter time. When I built my 750F2 I was able to re-use the loom and switchgear and the wiring was simply connect black to black etc. Done in a morning and right first time. I'm thinking this week I will go to the lock-up and bring my other 750 home, take the headlight off and see if I can copy what's in there onto the K5 (the wiring diagrams looks virtually the same).
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Going back to basics, start with the RH switchgear
1 does it have a lights on/off
2 1,2 or 3 wires to starter button
3 what colour wires go where
Its this bit that buggers up most wiring faults
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Thanks Bryan. Not in the garage now until Tuesday, will check and get back to you. Thanks for the help.
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Hello,in your start of this topic you post a colour wiring diagrame.Where can this be found?
I am shortly wiring up a K5.
Ta
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It's in the back of the Clymer workshop manual.
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Thanks for that.
The clymer manual that I looked at is B/W,is yours a special edition?
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Mine is the 8th edition 26th print run. In other words the latest edition last revised in 2010. It says Colour Wiring Diagrams on the front cover. Hope that helps.
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Does the high/low switch have a neutral position Roy?
Bugging the hell out of me why they show a neutral position if it doesn't have one, also poor attention to detail that they got the contact information wrong on the high/low diagram, you'd expect better from such a well known producer of these books.
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Can't get into the garage until tomorrow afternoon, the doors are blocked with a trailer. Will get back to you tomorrow as it's bugging me as well. Woke up at 3am this morning and the bugger popped into my head, that was it for sleeping.
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Just been studying that wiring diagram Roy and the design Honda did is terrible. Yes, the fuse box has 3 fuses, just like the 550F has, however everything runs through the main 15A fuse, if that blows the other 2 fuses are dead. Surely the idea is to isolate certain parts of the wiring so that in the event a fuse blows at least some other parts still work. Imagine your on a dark unlit motorway or even worse a side road with loads of bends, the main fuse blows, suddenly all the lights go out, your still doing 70 and have no idea where the road is going. IIRC on the 550F if the main fuse blows the lights stay on, if the lights blow the engine still works, how is that not a better system? and if so why fit such a bad system to a K5?
TBH it wouldn't be hard to convert it to something like the 550F system, disconnect the inlet wire from the headlight fuse and wire it up to the red wire that's unused from the stater solenoid. At least you'd still have a headlight working if the main fuse blows.
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I couldn't agree more Ken. It's all poorly designed. I mean, who in the world uses black for live feed
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I've been puzzling through this with everyone else.
The earlier 750's only had one fuse - 15A; this setup is no different really as all the power comes through fuse to the the key switch and then to the lighting and other circuits. So if the main fuse goes, there's nothing
Here's a wiring diagram schematic that seems to be the same asa the one Roy posted, but it has the connection in the dimmer switch correct. The colours are also a bit easier to identify.
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I have a question, though; how many positions are there on the indicator switch? What are the L1/L2 and R1/R2 about? L2 and R2 give you the buzzer and L1 and R1 don't. Is it held on position 1, for a short flash, and locked in position 2 for a longer flash?
I had a similar problem when I changed the handlebar switches on my K2 for later ones. I started with the switches and worked out what each individual switch position would do - e.g. turn on one indicator at switch and see which 2 wires were connected - grey + orange or light blue. Once you know this you can connect the switch wires to the loom wires to do what you want them to do.
Now the white wire from my RH switch (Low beam) turns on the pilot light; the dark blue wire (high beam) goes across to the LH switch to the Hi/Lo/PA switch.
I used a whiteboard and coloured markers as I went along to record everything. Took ages! After it all I drew a schematic using Powerpoint. I won't attach it here to avoid confusing people, but happy to share it by PM if anyone wants to see it.
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AFAIK Sean the R/H switch on the USA K5 just does on/off, nothing else. All it does is turn on the lights which in turn feeds the fuse that controls the main lights, this only has Hi/Lo so no neutral position. The L1 and R1 are when you hold the switch across with your thumb, for when you don't want the indicators to stay on, like passing a car or as you say a short flash. The L2 and R2 are when the buzzer sounds which is why the buzzer operates as it's to remind you to switch them off.
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If I understand that wiring diagram correctly, the headlight on/off switch is redundant; power to the hi/low switch comes in there on a Br/R wire from the general Br/W lighting wire. The On/Off switch connects the lighting circuit to the black power circuit, but the former is already connected at the ignition switch.
According to "Honda 750Expert" the switch was removed for US K6 models. An extract (he shoe thing is 130+ MB) from his book/manual is attached. You can get it complete here:
honda750expert.com (http://honda750expert.com)
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No I don't think you're understanding it correctly Sean. I can't see a brown/red at all unless that wire coming in from the 7A fuse is the brown red, just looks brown to me on my PC. Either way that fuse get's it's power from the brown/white circuit, (it's an internal connection inside the loom) which is powered by the headlight on/off switch,(which gets it's power from the standard black wire feed on Hondas) the brown/white circuit feeds the bulbs in the speedo/tacho, feeds the ignition switch so it powers the brown wire when the switch is on, which in turn powers the fuse for the rear light and also runs a feed down to the indicator switch so that when the indicators aren't working it powers the running lights the yanks got. As well as of course feeding the main light fuse due to the internal connection.
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Thanks for all the input to this thread it's been a great help.
I spent two full days almost pulling my hair out with frustration. I had everything functioning but just couldn't turn off the headlight, nor were the lights running through the 7A & 5A fuses. Part of the problem was the brown/white connection going to the 7A headlight fuse (brown/red) was female to female so I ignored it. I went to the lockup and brought back the original harness, it's knackered but still as it was taken off the bike. On the female to female connection was a 50mm long male to male connector, mystery solved. After connecting that, the return from the fuse box black/brown connects to black/brown to the dimmer.
I now have fully and correctly functioning electrics. After two days off and the help you guys gave, the penny dropped straight away. There is no neutral position on the dimmer, no idea what that was all about (the diagram is wrong here, on low it should show brown/green connecting to white). There's only one position on the indicator switch so orange/white and light blue/white remain unused. The brown cable for the buzzer is missing completely, but I don't need to worry about that. I have tested every function on the bike including power to the coils turning on and off with the right hand kill switch. I even turned everything on and removed the fuses one at a time to double check it kills the correct things.
I hope the above explains the situation as it's pretty hard to convey what's going on with electrics, if I missed something just ask. It's all a bit birds nest in the headlamp just now along with some bad connectors. But now it's all connected I will go through it one cable at a time and make everything good. I will be glad when it's all buttoned up and the headlight is on to be honest, it's been a bit frustrating.
Once again thanks for all the help
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Good news Roy. Always a relief when things fall into place and work as they should. :D
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Pictures like that one always look scary to me !
Cheers
Dennis
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Very well done Roy! I remember when I did mine with the new harness, connected up everything and when I activated the left indicator the rear right lit! 🥵🥵 but one by one I got there. Very satisfying when everything works then.
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To be honest, any time you avoid smoke and blown fuses is a win. Don't think I will be taking up auto electrics any time soon.
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Although all is now well, a mystery is still lurking in there. There's a brown wire that runs from the 5A fuse to the back light, that's the feed to the rear light not the brake light. That brown wire is connected inside the loom to a brown wire that runs into the headlight bowl, it has a female connector on it. I have left this wire unconnected. For what purpose would a rear light feed run to the headlight area, it's also not shown on any diagrams. Pretty sure I haven't missed anything, but that said it's been put in there for some reason? Another mystery to keep you up at night.
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Hi Roy! Anything to do with parking light? Second position on ignition switch.
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That was my first thought, but what does it connect to, and why isn't it on the diagram. Incidentally, I did test the ignition key in park mode and the rear light comes on as expected.
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That was my first thought, but what does it connect to, and why isn't it on the diagram. Incidentally, I did test the ignition key in park mode and the rear light comes on as expected.
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You mention the rear light works in park mode what about the front side lamp?
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That was my first thought, but what does it connect to, and why isn't it on the diagram. Incidentally, I did test the ignition key in park mode and the rear light comes on as expected.
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That’s same as mine, I didn’t have anything to wire up to at the front end, no side light. I can only assume park light was wired to running lights which these had initially.
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That was my first thought, but what does it connect to, and why isn't it on the diagram. Incidentally, I did test the ignition key in park mode and the rear light comes on as expected.
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You mention the rear light works in park mode what about the front side lamp?
Don't have the facility on my replacement indicators for that Ted. I think it's staying unconnected.
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If your headlamp has no facility to fit a side lamp would it be sacrilege to fit a separate subtle LED lamp?
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Although all is now well, a mystery is still lurking in there. There's a brown wire that runs from the 5A fuse to the back light, that's the feed to the rear light not the brake light. That brown wire is connected inside the loom to a brown wire that runs into the headlight bowl, it has a female connector on it. I have left this wire unconnected. For what purpose would a rear light feed run to the headlight area, it's also not shown on any diagrams. Pretty sure I haven't missed anything, but that said it's been put in there for some reason? Another mystery to keep you up at night.
If you look at that thematic - done by one of the guys on the US site - I posted up above, there is a brown wire running from the ignition switch which branches off backwards BUT also has a branch going to the headlight bucket with an unused female connector at the end.
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If you replace the headlight at some point in the future and you get one with a parking light or side light at least you know where to connect it to. The existing headlight halogen or that god awful big normal bulb?
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Whatever else may be wrong with the loom, they certainly gave you enough length; my wires are barely long enough to get into the headlight bucket!
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It was as long on the other end, I had to pull it up a bit into the headlight to get the many connections correct behind the side panel. Will have to shorten some of the cables or I won't get the headlight in. Usual pattern parts, they appear to go to a lot of trouble to get it wrong. Bewildering really, it's as easy to get it right as wrong.
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The brown/white is for the small park light, which is not fitted in US but is actualy a legal requirement in UK as according to construction and use/mot it is an obligatory light, unlike the headlamp which doesnt have to be there but if it is it must work.
Good old english lawmakers, no sense, no idea
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That means then that the front parking light will be on whenever the rear light is on, ie when riding at night. That can't be right?
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Every vehicle I have owned has the front side lamp illuminated when the rear lamp is on including when the headlamp is on dip or main. I believe the law calls them positional lamps.
Only DTRL's have changed that slightly - some dim at night etc.
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Agree with Ted, they are designed to have the side light lit whenever any lights are shown, including as Ted says dip and main.
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Fair point. If only I had a side light.
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A side light my kingdom for a side light I hear someone cry! :P :P :P
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I did wonder about some period looking daytime running lamps for my 750 but never managed to source any.
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The brown white IS for the front parking light but the yanks use sealed beam headlamps without one .
The orange/white and blue/white are for the front running light in the US front indicators, not legal in UK so leave them loose