Topic: wiring on '78 CB750K

[medic09]

Last time around El Cheapo suggested I just get to work with the wiring diagram.

I'm almost lost in the wiring diagram, sorry. 

Here's what I've got for a problem:

guages don't light up.  when I operate the turn signals, the guage lights operate in sink with the blinking turn signal.
no tail light.  no right parking light, rear.  brake light works fine.

I've tried tracing wires, but I'm pretty lost.  Anyone got some good guidance?


Thanks!

[medic09]

sorry, that's operate "in synch" with the blinkers...

[flatblack]

I have a '78 750K also...

In looking at the wiring schematic, I'd bet you have something crossed up in the wiring under the seat. Check the runs of the solid dark green wires and the green w/ yellow tracer wires. The dark green ones appear to ground the front and rear turn signals, tach/speedo lights and tail light. The green/yellow wires are for the brake light.

If that's not it, then something's FUBAR'd in the headlight bucket involving the same circuits.

HTH...

fb

[bryanj]

You shouldn't have ANY parking lights rear EXCEPT in the red rear light

[medic09]

Flatblack,
Thanks, I'll start there.  I started in the headlight bucket (where someone made a mess of connecting and tucking stuff in) with the diagram, and nearly got dizzy!  There's not enough length to just pull the wiring forward out of the  bucket so that I can easily sort through it.  Under the seat will be an easier place to check and rule out.  'Course, we just may be FUBARed up front, as you noted.

[medic09]

You shouldn't have ANY parking lights rear EXCEPT in the red rear light

bryanj,

Thanks!  PO put hard bags on the bike, with the turn signals on the back of the bags.  With the key in 'Park', I've got my rear light lit, and one rear signal lit (actually, both lit the other day, but how it's back to one).

[hcritz]

Hey Medic09...
When you get strange things like that going on...it could very well be a bad ground...the instrument lights coming on with the turnsignals etc. If the is no ground...sometimes the current will find it's way to earth through another bulb filament.
If the diagrams give you a headache...try drawing each circuit up separately on a sheet of paper...makes it easier to follow sometimes.
Once you break it down into systems... Brake lights...head and tail light... it's really a pretty simple system.
Good luck!!!

[medic09]

Thanks so far, all!

Here's the update.  I looked under the seat.  Found that PO had clipped two wires (R and L) from the rear signals to the Brown wire.  I unclipped those.  That killed the 'additional' parking lights (that addresses bryanj's comment, though additional light probably weren't a bad idea).  Checked all connections at the taillight, and under the seat.  The bulb is fine.  The brake light filament works, and the parking light filament (would also be the tail light filament?) works.  Turn signals work.  Connections seem okay, or the lights wouldn't work.

Still no tail light.  Still no gauge lights.  Gauge lights still come on and blink with in synch with the turn signals.

Next? 

[bryanj]

Gauge lights and rear light should connect to a brown/white wire (I think!) in the headlamp bucket(might be just brown--I dont have that wiring diagram) and the headlamp on/off switch--We are talking UK models now--- puts power to the dip switch and to this brown wire, As thge US have permanently on headlight I am unsure as to where this connection is  BUT if you find the wire that takes power from the start button to the dip switch (black and red?) and temporarily connect the brown into this you should get headlamp and rear lamp along with gauge lights.

hope this helps

[medic09]

Thanks, bryanj!

I *think* the brown wire (at least running from the back), ended in 'nc'/no connection?  I'll have to check.  I do understand the idea.  Over the winter, I'll probably have to take time off of my project and sort all this out from the start.

I'll report back if I find out anything in the next little while.

[medic09]

Okay, I do know this is getting tiresome (how do you think I feel?  )...

Pulling into my garage tonight I notice that when the brake light comes on (remember, no tail light but I do have brake light), it also shine clear down on the license plate.

Isn't that supposed to be how the taillight works?  Or would the brake light illuminate the plate, just because the fixture is clear on the bottom?  Or do I have another clue to what got switched?

Arrrrgggghh....

[medic09]

Okay, so I looked under the left sidecover...there's crispy, fried looking wires in there!   

Am I correct in thinking that I probably need to consider replacing the wiring harness?  Will I be sorry to take on such a project?  Any idea where to find one reasonably priced for a '78 CB750K?  There's a few on Ebay, but I don't know if they're in better shape.  New, OTOH, is pretty expensive.

Thanks!

[bryanj]

Unlkess Dave Silver does a pattern loom i have no idea where to get one.
As long as you are methodical and carefull it should only take 2-4 hours to replace as all the wires go colour to colour

[750goes]

You got no problems at all, you got something that works - just connected wrong...or not clean

have a look at my mess, and my achilles heel is definitley electrics... but with lots of help and lots of fuses,
I got it working again - the left sidecover area is a real conglomeration of nasty stuff so be  careful in there - don't play with anything if you are not sure, major damage can happen real quick...ask lots of questions and......good luck 

mostly the wires if the harness is not too trashed just match up to each other like yellow to yellow etc.... just make sure of all the dark green ones (earth) are clean and tight... cause of most problems too...

[medic09]

Thanks!

So, you all find replacing wire-by-wire better than laying in a harness from another bike or a new (expensive) one from someplace like HondaPartsDirect?  Some of these wires entering the area under the left side cover a completely crispy.  One just broke (yellow) with me just pulling it aside a bit to look at it... .  I spliced it together (sort of) for now, with an electrical tape wrap, but these wires do not inspire me with confidence.  And this bike is my daily ride to work and school.  I'd hate to be stranded on a cold dark morning on the Interstate instead of writing a MedSurg exam (on second thought, cold and dark doesn't sound so bad... ).

Remember, I'm a mechanical and electrical IDIOT, learning as I go along.  I do ask questions, but it's still dependant on my learning curve.

Thanks!

[dusterdude]

i would say if you can find a harness in good shape for a price you are willing to pay,buy it.

[Jinxracing]

Remember, I'm a mechanical and electrical IDIOT, learning as I go along.  I do ask questions, but it's still dependant on my learning curve.

If you're uncomfortable with doing the harness all at once and the diagrams don't make sense to you, the "one-wire-at-a-time" idea is something to consider. By the time you're done you'll know it inside-out and be a wiring guru!

[jdpas29]

Remember, I'm a mechanical and electrical IDIOT, learning as I go along.  I do ask questions, but it's still dependant on my learning curve.

If you're uncomfortable with doing the harness all at once and the diagrams don't make sense to you, the "one-wire-at-a-time" idea is something to consider. By the time you're done you'll know it inside-out and be a wiring guru!

that's basically what i had to do....  i had a conglomeration of burnt/not-burnt/partially burnt wires.  i just replaced all the ones i wasn't comfortable with and left the others.  some jack-leg ripped the fairing off of my bike at some point and totally messed up the signals and headlight wiring, but if you have the appropriate wiring diagram and some patience, you'll get it right.

[medic09]

I hear what you all are saying...but wouldn't it just be easier and surer to lay in a complete harness and plug stuff in? 

[750goes]

If you are going to put in a NEW harness, are your sure it is the right one, and is your bike in ORIGINAL electrical condition, with the right bits and pieces to connect to - if so, new harness is good, if not - you may be wasting your time and end up with a botched system you have to cut and paste to get working...

better off time wise probably getting someone else do it for you

better off money wise to check all the wires and test them yourself - it is not hard -just fiddly and a bit of time...

 

[medic09]

better off time wise probably getting someone else do it for you
 

It's too labor intensive...this bike is my daily commute so I need it running, but I can't pay the labor cost for a relatively simple job.  'Course, over the years I've paid labor costs to repair what I"ve botched... 

[medic09]

Maybe another clue...?

This morning, while warming up the bike (in the dark, at 6:00 AM, 30 degrees F outside), I noticed the right front signal wasn't on (running light).  When I came back a few minutes later, it was.  Maybe there's a short here that has to do with my lack of taillight?

A mechanic here in town said, off the top of his head, that it might actully be in the right switch assembly (starter/cut-out).

Any thoughts?  I'll still probably change the whole harness when the part gets here...