Author Topic: wiring diagram help  (Read 4072 times)

0 Members and 2 Guests are viewing this topic.

Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
wiring diagram help
« on: January 06, 2011, 10:40:02 PM »
1978 CB750 F3

On my project bike I was installing a new blade type fuse box and all new connectors and plugs. My problem is that one of the wires is missing on the wire harness that plugs into the 5A fuse. Specifically the brown/blue stripe wire. Everything else seems to be intact. I am not sure what happened here but apparently one of the PO's removed it. Tracing the wire on the diagram it looks to me like its needed to power the tach and speedo light. Is this correct? Can I just replace the wire on the plug and splice into one of the black wires? Thanks for any help.

http://data.sohc4.net/WD750/Honda%20CB750F%201978.jpg


Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
Re: wiring diagram help
« Reply #1 on: January 06, 2011, 11:06:49 PM »
Here is the plug that plugs into the fuse box. The two red wires on the left go to the 15A fuse. The two brown/red stripe wires on the right go to the 7A fuse. The center brown/white stripe wire goes to the 5A fuse and the missing wire is what I am needing to fix. I need to make sure I can put a wire in the empty slot and splice it into one of the black wires in the harness to complete the circuit.

« Last Edit: January 06, 2011, 11:09:44 PM by BWJ »

Offline Toxic

  • Expert
  • ****
  • Posts: 1,200
Re: wiring diagram help
« Reply #2 on: January 07, 2011, 04:44:43 AM »
Can you not peel back the po's e-tape until you find what's left of the missing wire?
There has to be a point at which you find the cut end or where that wire would normally be attached and then just connect the wire you need.  That way you are at least returning the harness to factory specs.

Offline Shoeboxjoe

  • Large Breasts
  • Enthusiast
  • **
  • Posts: 184
Re: wiring diagram help
« Reply #3 on: January 07, 2011, 07:34:39 AM »
That plug looks like the plug to the main switch, not the fuse box. And it looks like it has all the wires you need. The brown w/ white stripe powers the speedo and tach lights.
1977 Honda CB750K Project IDK yet
http://forums.sohc4.net/index.php?topic=121669.0

SOLD 1976 Honda CB750K Cafe project
http://forums.sohc4.net/index.php?topic=52576.0

1964 Honda Trail 55 (C105T) Custom project
http://forums.sohc4.net/index.php?topic=64962.0

1967 Norton P11 (restoring for father-in-law)
1978 Ford Fiesta (at body shop!)

Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
Re: wiring diagram help
« Reply #4 on: January 07, 2011, 09:57:26 AM »
The harness has all the tape removed. There is no evidence of where the wire used to be. And no the plug to the main switch is at the other end. This is definately the plug for the fuse box....

Offline Shoeboxjoe

  • Large Breasts
  • Enthusiast
  • **
  • Posts: 184
Re: wiring diagram help
« Reply #5 on: January 07, 2011, 10:31:34 AM »
Doh, i guess it's not the main switch, there is no black wire. Well if it's the brown w/ blue stripe you're missing wouldn't that be the power to turn signal buzzers, front stop switch, and neutral/Oil pressure lights?
« Last Edit: January 07, 2011, 10:34:38 AM by Shoeboxjoe »
1977 Honda CB750K Project IDK yet
http://forums.sohc4.net/index.php?topic=121669.0

SOLD 1976 Honda CB750K Cafe project
http://forums.sohc4.net/index.php?topic=52576.0

1964 Honda Trail 55 (C105T) Custom project
http://forums.sohc4.net/index.php?topic=64962.0

1967 Norton P11 (restoring for father-in-law)
1978 Ford Fiesta (at body shop!)

Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
Re: wiring diagram help
« Reply #6 on: January 07, 2011, 10:51:48 AM »
OK, just snapped a couple more pictures to help solve the puzzle.

Here is the back of the OEM fuse box 6 wires: two red, two brown, two brown w/red stripe


Here is a shot of the rear portion of the harness that is mounted near the battery box. The plug in question that goes to the fuse box is the plug in the bottom center of the picture



This is the forward section of the harness. The plug in middle top section of the picture goes to the ignition switch.


The five wires on the bottom of the picture here go to the plug in question. By looking at the wiring diagram it looks like my missing wire (brown with blue stripe) may need to be spliced into the crimped section with the three black wires shown here. This is what I need help with. Just want to make sure I get the wire in the correct place.


« Last Edit: January 07, 2011, 10:58:56 AM by BWJ »

Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
Re: wiring diagram help
« Reply #7 on: January 07, 2011, 10:57:55 AM »
Doh, i guess it's not the main switch, there is no black wire. Well if it's the brown w/ blue stripe you're missing wouldn't that be the power to turn signal buzzers, front stop switch, and neutral/Oil pressure lights?

I believe your correct. However it seems that this wire is needed to complete the circuit to power the horn, speedo lights ect. At least thats the way I understand the diagrahm.

Offline Shoeboxjoe

  • Large Breasts
  • Enthusiast
  • **
  • Posts: 184
Re: wiring diagram help
« Reply #8 on: January 07, 2011, 11:39:53 AM »
After going through the diagram i think you're correct. There should be a bullet connection in the headlight bucket though that this previously connected to the black wire. So yea splicing this in here should accomplish the same thing according to the diagram.
1977 Honda CB750K Project IDK yet
http://forums.sohc4.net/index.php?topic=121669.0

SOLD 1976 Honda CB750K Cafe project
http://forums.sohc4.net/index.php?topic=52576.0

1964 Honda Trail 55 (C105T) Custom project
http://forums.sohc4.net/index.php?topic=64962.0

1967 Norton P11 (restoring for father-in-law)
1978 Ford Fiesta (at body shop!)

Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
Re: wiring diagram help
« Reply #9 on: January 07, 2011, 11:52:15 AM »
Thanks for your help joe!

Offline Shoeboxjoe

  • Large Breasts
  • Enthusiast
  • **
  • Posts: 184
Re: wiring diagram help
« Reply #10 on: January 07, 2011, 12:20:14 PM »
lol Sounds like you know what you're doing. Need no help from me.
1977 Honda CB750K Project IDK yet
http://forums.sohc4.net/index.php?topic=121669.0

SOLD 1976 Honda CB750K Cafe project
http://forums.sohc4.net/index.php?topic=52576.0

1964 Honda Trail 55 (C105T) Custom project
http://forums.sohc4.net/index.php?topic=64962.0

1967 Norton P11 (restoring for father-in-law)
1978 Ford Fiesta (at body shop!)

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 13,810
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: wiring diagram help
« Reply #11 on: January 07, 2011, 08:55:35 PM »
Splicing to the Black won't hurt, but it's curious that the wire is missing. Some riders who removed this wire were simply de-powering the turn signals on the F2/F3/K7/K8 bikes, but it also turns off the instrument lights in so doing...  :-\

Check your tailight (if stock?) for the wire colors. If it has the BROWN and BROWN/WHITE  wires with the GREEN 'ground' wire, your harness may have been using the instrument light circuit to power the running tail lamp, which appeared in some bikes near the end of production (leftover parts, maybe, or some from other models that fit, was Honda's practice in those days). This was more commonly found on some F0 bikes, but I think maybe the wire harnesses get swapped around in boneyard trades, sometimes? I recently fixed up a nice F1 that had a K5 harness in it, which looked this way.

I saw quite a few K6 bikes with F0 harnesses "in the day", which really confused us at out-of-the crate assembly times, since it was not yet in the manuals. I also know of some DOHC 750 harnesses appearing in the last F3 bikes: these were visible by a different-looking fuseholder on virgin F3 bikes (rectangular, same hole spacing). The wire colors on the fusebolck did not match the manuals.

The other 'missing link' you may run into is the "spliced wire" change on the power plug, which can affect the rest of the harness with a missing BROWN/WHITE wire: the Brown/White and Brown are spliced together in these harnesses, about 1" inside the black wrapping, and they run through the bike as Brown only. These appeared (occasionally) on the late F1 and early F2 bikes, the K8, and on the first year of DOHC750 bikes. They all use the same steering-head-mounted keyswitch and plug.

Now you know why I omitted the 1976-and-later wiring from my first book...  ::)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline brandEn

  • Old Timer
  • ******
  • Posts: 3,205
Re: wiring diagram help
« Reply #12 on: January 07, 2011, 09:24:36 PM »
Thanks Mark! I dont have the stock tail light assy so I cant check. But just to make sure of what you said.... If I add the wire to the plug and splice into the black wires everything should work like it supposed to?
« Last Edit: January 07, 2011, 09:30:57 PM by BWJ »

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 13,810
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: wiring diagram help
« Reply #13 on: January 07, 2011, 09:36:02 PM »
Thanks Mark! I dont have the stock tail light assy so I cant check. But just to make sure of what you said.... If I add the wire to the plug and splice into the black wires everything should work like it supposed to?

Yep, that will at least make the circuits power up.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com