Topic: New wire harness headlight bucket strategy?

[Popwood]

Starting from back of 750 K5, I’ve switched out old for new up to the headlight bucket mess of wires. seems all the wires must now be disconnected from old harness to insert the new harness into the bucket. Problem is, PO got “creative” with some mix and match wire colors years ago. Any secret sauce to tackle this problem. would seem a great leap of faith to just undo it all and hope for the best.

[Don R]

 I'd try to ID the new colors before taking it apart. Follow the wires back to where they are original, or see what color they should be. Maybe make some tags.
 I like to print out the full color wiring diagram as big as possible. I was able to make it two pages once and glued it to a piece of card material like a beer carton or cereal box. The Old man Honda website had them easy to download once.

[HondaMan]

Are the wire harnesses from the handlebars still the OEM versions, or were the switches on those bars also changed out? Reason I ask: most of the aftermarket switches I have installed followed the main wire harness for color codes, so it was pretty straightforward to match things up. One thing that is consistently NOT simple in the aftermarket K4/5/6 RH switches is: there are often 2 Black wires coming from that switch in aftermarket switches. One of them powers the RUN-OFF kill switch while the other powers the START button. If there are 3 Black wires coming from the RH switch: that 3rd one powers the Lights ON-OFF switch that some of the aftermarket switches have. Honda discontinued that ON-OFF switch twice in production 750s, once in 1974 and again in 1976, so your bike may have one (if OEM or with certain aftermarket RH switches).

Also: sometimes the 2 wires from the RUN-OFF switch are not the regular Black and Black/Red, but one of them might be Black/Yellow instead of Black/Red. The other one for that switch should be Black: in some switches there is only 1 Black wire that feeds the RUN/OFF and the START button. So far, in all aftermarket switches that I have installed, there were at least 2 Black wires in the RH harness, a good thing. Long ago, though, I came across a 750K3 RH switch that had a single Black wire feeding the RUN/OFF, Lights OFF/ON and the START button: since the owner had both 3-ohm spark coils and a 100 watt headlight beam, the wire was melted in several places, causing an intermittent short and blowing the main 15A fuse when the handlebars got turned (to the right). Hopefully your RH switch harness has at least 2 Black wires in it?

[Popwood]

Thanks for the suggestions and heads up on aftermarket RH switches. That switch on my bike is clearly newer looking and there was an old switch that came in a parts box when I bought the bike in 2008. What I’m facing in the headlight bucket is not just a bunch of wires, but a wad of wires that are all “knotted” together making it impossible to separate into any organized groups. So I think what I’ll do is begin disconnecting like colored wires that will be easy to reconnect with the new harness like colored wires. These are probably 75% of all the wires. Then I’ll be able to better separate the rats nest and be better able to make sense of the mismatched color connections. Will then label those exceptions and study what subharnesses they connect to. One thing I’ve been a bit surprised on this project— how many components I’ve had to remove from the bike, mostly the battery box and those under the left side cover, in order switch the new harness connections with the old. I probably could have left them in place, but it would have been harder and more time consuming with them in place.

[newday777]

Thanks for the suggestions and heads up on aftermarket RH switches. That switch on my bike is clearly newer looking and there was an old switch that came in a parts box when I bought the bike in 2008. What I’m facing in the headlight bucket is not just a bunch of wires, but a wad of wires that are all “knotted” together making it impossible to separate into any organized groups. So I think what I’ll do is begin disconnecting like colored wires that will be easy to reconnect with the new harness like colored wires. These are probably 75% of all the wires. Then I’ll be able to better separate the rats nest and be better able to make sense of the mismatched color connections. Will then label those exceptions and study what subharnesses they connect to. One thing I’ve been a bit surprised on this project— how many components I’ve had to remove from the bike, mostly the battery box and those under the left side cover, in order switch the new harness connections with the old. I probably could have left them in place, but it would have been harder and more time consuming with them in place.

In the headlight bucket of the K5 watch for the short jumper, 2"-3"(?), might be a brown and white that has a black piece of heat shrink on one end (or maybe a yellow with red stripe wire??) while unplugging the wires, take pictures of where it plugs in so you don't forget.

[PeWe]

It will be easier if you use the circuit diagram, a buzzer (or ohm meter), tape to write on.
Verify all switches, mark what they do.

Then mark the main harness wires.
I used both simplified color diagram and the more detailed Honda.

K6 has a jumper between black and brown (or brown/white). I do not know if K5 has it too. Possible to find in Honda diagram if looking for it.
If not connected no gauge illumination.

Too easy to scrap that jumper with the old main harness.

[newday777]

It will be easier if you use the circuit diagram, a buzzer (or ohm meter), tape to write on.
Verify all switches, mark what they do.

Then mark the main harness wires.
I used both simplified color diagram and the more detailed Honda.

K6 has a jumper between black and brown (or brown/white). I do not know if K5 has it too. Possible to find in Honda diagram if looking for it.
If not connected no gauge illumination.

Too easy to scrap that jumper with the old main harness.

My K5 has the little Jumper

[rotortiller]

Advice, ohm meter, wiring diagram, and a bit of patience. Electrically they are pretty simple machines after a bit of study.

[kyle750]

Electrically they are pretty simple machines after a bit of study.

I just learned that a modern wide body passenger jet can contain over 500 kilometers (310 miles) of wiring When I first started troubleshooting wiring problems on my CB750 I was totally overwhelmed but quickly discovered that the electrical system is relatively simple, straightforward, and easy to fix. When checking the wiring I kept a written log of every connection checked (color codes, etc) so I was not double checking or missing any wires. Rather than think about the entire snake pit once I could break it down mentally to just one wire at a time the task became quite manageable. 

As someone who is new to working on bikes I was completely intimidated by the mess of wires in my CB750  and dreaded a short in the electrical system.    With the generous assistance of other forum members and a little hands on experience I am now actually looking forward to working on the old wiring in my CB550.

[rotortiller]

Because of that aerospace complexity most wires in that industry are generally not color coded and are of the same white color. Each wire gets a tiny number etched into it that is a code for which system it belongs to, gauge, polarity, segment etc. Wire schematics are coded the same. Many wires have a similar but not fully identical number in the same circuit. SOHC color coded electrical even when acting up can be enjoyable low stress fun. Many of us like our low tech and snail speed uncomplicated tanks for that. Our old tanks are a bit more complicated than say a utility trailer but not by much, however they are a great learning and social tool in the hobby format.

[bryanj]

Reminds me of Citroens in the80's, all wires were yellow with a white loose sleeve at the ends that had a code, at least when they were new and clean they did!!

[MauiK3]

MANY years ago as a young Marine Machinist I stopped by where a (to me, then) old electronics guy was working on a wire way in a submarine that must have been12" in diameter, just full of small wires (not power). I asked him how he keeps it all straight and he looked at me rather annoyed and just grunted out "one wire at a time". I moved on to my work .

[HondaMan]

MANY years ago as a young Marine Machinist I stopped by where a (to me, then) old electronics guy was working on a wire way in a submarine that must have been12" in diameter, just full of small wires (not power). I asked him how he keeps it all straight and he looked at me rather annoyed and just grunted out "one wire at a time". I moved on to my work .

I knew one of those guys who was on nuke subs for 8 years.
He said that until the wires entered the 'device' (like a CRT screen or some sort of console or junction box) that there was no ID anywhere on the harness wires. They used a 'tracer', which was a very small clamp that clipped over the wire at one end of the sub and induced an oscillation ("tone") into the wire that could then be followed with a 'sniffer' that also clamped onto the wire, showing the "tone" on a portable 'reader'. They had 3 on the subs he was on, in their toolroom.

Kind of overkill for a bike with 40 wires, but still kinda cool?

[bryanj]

You can use two people each with a phone handset,
One person puts one wire of handset to ground and other on a wire and starts whisteling/singing/talking
Other persong has one wire to ground and keeps moving the other accross wires till he hears No1