Topic: Honda CB750 Wiring

[kyle750]

I was expecting a hornet's nest of wiring problems on a 55 year old bike but so far it's been fairly simple and easy.  Honda's wiring and color coding system is very intuitive and straightforward. I decided to start with the easiest first hoping to gain some knowledge while trying to slowly build confidence as I go along.   

Started with the tail light.  Removed the previous rewiring. Sorted the green, brown, and green with yellow stripe to the tail light and then the turn signals to orange and blue. A few of the connectors needed to be tightened and now all the bullet connectors are inserted solid and tight.

I'm sure it will get more complicated when I take a look at other electrical components on the bike.     

Rewiring by the previous owner when the bike first arrived 

[kyle750]

Removing the old wiring, inspecting original vintage Honda replacement wiring and attaching to the tail light, pulling the wiring through the fender tunnel, and attaching to the connectors under the seat.

Late Edit:  The black wire in Photo 2 was not an original Honda wire and I finally was able to track it down to the left turn signal where the original turn signal wire was cut very close to the mounting bracket? Both rear turn signals were in poor condition.  I bought correct short stem original vintage replacement turn signals both with original lead wires.

[Don R]

 I changed a US delivered CB400F to euro/asian headlamp and switch with the park light. The connections seemed really difficult until I realized all I needed to do was remove the us bike jumper. Then it was all color to color matching. The park light worked great, it was a Marchal headlight from Yamiya and it light up nice with a yellow LED bulb.

[kyle750]

The tail light 

[Deltarider]

I changed a US delivered CB400F to euro/asian headlamp and switch with the park light. The connections seemed really difficult until I realized all I needed to do was remove the us bike jumper. Then it was all color to color matching. The park light worked great, it was a Marchal headlight from Yamiya and it light up nice with a yellow LED bulb.

Don, could you please guide us to that LED light? I myself have chosen a 21W halogen Ba9s for DRL, which evenly illuminates all of the reflector and so is well noticed in daytime. If a LED like yours can achieve the same, it would mean a further improvement. Unfortunately the LEDs that I have come across, either showed poorly like in the pic of the truck or they were much too bulky and installment would have hindered the main 60/55W H4 bulb spreading its light.

[kyle750]

A quick question to the Honda Community.  Rear turn signals have a single source black wire with colored coded ends (orange and blue).  Is there supposed to be a ground wire also?  IIRC the front turn signals have ground wires attached to  threaded bolts inside the headlight bucket. Thanks!

Late Edit:  I just noticed small hook tabs visible on both sides where the fender mounts to the frame.  Are the hooks to be used as a helmet holder where the D-ring on the strap slips over the hook? 

[Deltarider]

A quick question to the Honda Community.  Rear turn signals have a single source black wire with colored coded ends (orange and blue).  Is there supposed to be a ground wire also?  [...]

It depends. Impossible to give an answer that's valid for all models. The appropiate wiring diagram is your friend.
Some models like the CB500 needed a dedicated wire for GND in the rear, because Honda had gone through so much effort to guard these lamps from vibrations, that a wireless path to GND was blocked by little rubber silent blocks.

[bryanj]

Not with the mounting bracket in your hand, which should be black not chrome,
Lamp base grounds to bracket, bracket to bolt, bolt to spacer, spacer to frame plus bolt threads

[kyle750]

Not with the mounting bracket in your hand, which should be black not chrome,
Lamp base grounds to bracket, bracket to bolt, bolt to spacer, spacer to frame plus bolt threads

Thanks Mate.  The chrome house shaped mounting brackets are original to the bike (this is for the CB750 and not the CB550).   I swapped out the old turn signals with replacement turn signals.  I just checked and the old turn signals also were single source black wires - no ground wires.

[kyle750]

I took out the square rubber inner liners from the backside of the turn signal chrome house shaped mounting brackets today and cleaned them up with degreaser, left them in the sun to soften the rubber, and then put on a thick coat of silicone grease.  More sun.  Just wiped them down and they are now soft and supple - no longer hard as a rock and brittle. Amazing this rubber is over 50 years old and it is still very usable and continues to work as intended.

[kyle750]

Removing the old wiring, inspecting original vintage Honda replacement wiring and attaching to the tail light, pulling the wiring through the fender tunnel, and attaching to the connectors under the seat.

Late Edit:  The black wire in Photo 2 was not an original Honda wire and I finally was able to track it down to the left turn signal where the original turn signal wire was cut very close to the mounting bracket? Both rear turn signals were in poor condition.  I bought correct short stem original vintage replacement turn signals both with original lead wires.

Correction:   I bought  vintage replacement turn signals both with original lead wires and mounted the heads on the existing fixed stems of the mounting brackets that were originally on the bike

[MauiK3]

You may find lots of crispy wiring up front. If it's too far gone a replacement harness may be in order at some point. Also, you can get a Honda style bullet connector kit if needed, they crimp on easily.

[kyle750]

You may find lots of crispy wiring up front. If it's too far gone a replacement harness may be in order at some point. Also, you can get a Honda style bullet connector kit if needed, they crimp on easily.

Both are excellent ideas.  Thank You.  I will look into a harness and a honda bullet style connector kit (I can already see how this would be extremely useful).

[Stev-o]

Late Edit:  I just noticed small hook tabs visible on both sides where the fender mounts to the frame.  Are the hooks to be used as a helmet holder where the D-ring on the strap slips over the hook? 

Yes, and my K4 has a label "helmet holder"

[kyle750]

Late Edit:  I just noticed small hook tabs visible on both sides where the fender mounts to the frame.  Are the hooks to be used as a helmet holder where the D-ring on the strap slips over the hook? 

Yes, and my K4 has a label "helmet holder"

Thanks Mate.  The later "helmet holder" label was clearly added for slow-witted blockheads like me 

[BenelliSEI]

Those chrome rear turn signal brackets are just black painted steel originally. They did come with a ground lead attached to the back of the large plate portion. The ground to the lamp body is made by clamping it to the post (make sure it is clean and bare). If the ground wire is broken off I usually run the wire right inside the lamp housing and ground it directly to same screw that takes the ground from the lamp body to the socket.

[HondaMan]

Some of the replacement turn lamp assemblies I've bought had a Black wire for the element, onto which I was supposed to add the Orange or Light Blue according to the side it was mounted. I guess this is the 'universal' part approach these days? The rear lamps (smaller filament) for some countries do not have to light up when the lights are on, but some countries required it for a while in the last century. Here in Colorado USA the rear lamps had to light up with the taillight from 1980 to 1986 when [we bikers rebelled and] the population took umbrage with it, because the bikes weren't built to support the loads. This State's DOT then backed off to "...if came as OEM..." mods to their laws.

I for one never rewired mine (750K2), as it was indeed unconstitutional to have to do so. That's why I still remember this little dust-up...

Many of the aftermarket lamps now come with the dual-filament bulb sockets regardless, so the user can wire accordingly.

[kyle750]

@BenelliSEI your CB750s always look stunning and the photo of the back of the bike looks perfect.  Beautiful black frame (I'm quessing powder coated),  chrome looks to be in superb condition, and the tail light looks like new.  I see you added  black sheath covers to the wiring - a fantastic finishing touch and also adds another layer of protection to the wiring.

100% complete perfection.  Beautiful work Sir!

[kyle750]

@HondaMan  Many thanks for the very interesting history on changes in tail light laws over the years.    I completely agree with you that forcing modifications to comply with newly mandated laws should be ignored.  Bike owners know what is best for their bikes not legislators sitting in a state capitol.

[kyle750]

I now understand the need for an extra outer layer of protective sheathing.  On close inspection I can see where one of the turn signal wires has rubbed against the mounting bracket and the outer black cover has worn down exposing the inner wire.   Not Good!

I will wrap the worn wire with electrical tape.  Later I will visit my local bike shops and see if they have some black sheathing I can scavenge from an old junk bike

[bryanj]

Heatshrink tube from fleabay or any decent auto electrician

[kyle750]

Thanks Mate.  Heatshrink in 2 different size diameters at the local 20 baht store.  Total cost $.60 cents.  Photo of the smaller diameter heatshrink on one of the turn signals.

Just hit it with the heat gun and zap!  Shrunk to fit tight, better protection for the old wire,  and looks like new.

Late Edit:   . . .  and looks a lot better than old time sloppy and gooey black adhesive electrical tape 

[bryanj]

There ya go, at my age there is not much i havent seen in the workshop, although modern cars are trying my patience, a £3000 internet enabled scanner to tell your car it has a new headlamp bulb before it will work!!!

[BenelliSEI]

@BenelliSEI your CB750s always look stunning and the photo of the back of the bike looks perfect.  Beautiful black frame (I'm quessing powder coated),  chrome looks to be in superb condition, and the tail light looks like new.  I see you added  black sheath covers to the wiring - a fantastic finishing touch and also adds another layer of protection to the wiring.

100% complete perfection.  Beautiful work Sir!

Thanks! I think that is the back of the S/C. It is black paint followed with a light clearcoat. I don’t see a ground wire coming from your chrome base plates. How are you getting a ground to the lamp?

[MauiK3]

I've purchased a lot of split loom and heat shrink from Amazon. Ignorant question: does Amazon work in Thailand?