Topic: Troubleshooting: Headlight Electric Issue

[highrpms]

Hello all.  This is why I love this forum.  Mostly all done and the ONE issue that is killing me with restoring this bike is the headlight does NOT work.  The bulb and headlight casing are brand new (dropped the oringal). 

Everything else in the left hand controls works perfect.  New batttery and all.  The horn, works. turn signal and turn signa, buzzer, works.  Headlight and highbeam are completely out.  nothing. nothing at the wires nothing. 

I am NOT eletrical wiz here by any means.  I know very little in fact but this is annoying.  (I know I know)  35 year old bike and this is my only problem to this point. 

Ideas? Solutions?
Thank you very much

Eric
(1976 Honda CB750K)

[TwoTired]

Did you check the headlight fuse?

[highrpms]

I thought I checked ALL fuses but I dunno? 
Do you know what part number that is in this diagram?

Sorry
Thanks!!!

http://www.bikebandit.com/houseofmotorcycles/1976-honda-motorcycle-cb750k/o/m9456

[TwoTired]

741323
(255289-001)

[highrpms]

yes all of them are fine... i checked them prior to bulb and housing

thanks tho i didnt know that was headlight only.

[TwoTired]

Do you have a wire diagram for your bike?
It's like a road map for showing electrical power paths.
With a voltmeter, you can track it's progress (or lack thereof) from source to destination.
When the "bridge is out" you can see it no longer gets to destination.

Cheers,

[highrpms]

i do.  i get a little confused when it gets to the left hand controls - and everything else in the control works. 

are they all run off the same power?  so if the horn and turn sgn and turn sgn buzzer and all work is the headlight? or it that a bad assumption? 

really appreciate your help...

eric

[TwoTired]

I assume you have a Honda Diagram rather than a Clymer generic.

Headlight power comes from the Key switch to the right hand control via the Black wires.
It is then routed through the starter button (interrupted when the button is pressed).  Power then moves on via the Bk/R wire to the Headlight fuse.  The wire from the fuse turns into Br/R on it's way back the left bar control connections.  The H/L switch then routes power to either the White or Dk Blue wires for the headlight.

Cheers,

[highrpms]

great thanks i will follow in that order. 
let the fun begin.  only issue with the bike is that i cant ride it to 2 wheel tuesday nights in the city right now. 

looking to cure that. 

much appreciated and have a great weekend!

Eric

[octagon]

following up on twotired's post - if you've been plugging and unplugging wires to change the headlight bucket, you should make sure your right side power switch connections are good.

[domer]

just my 2 cents, but just cause the fuse was ok before you put the light in doesnt mean its ok now. get a multimeter and google how to use it, it will become your best friend!

[Steve F]

yes all of them are fine... i checked them prior to bulb and housing

thanks tho i didnt know that was headlight only.

Please don't take this the wrong way, I'm not saying that you don't already know this but, most people often check the fuses by just a visual check to see if the element is still in one piece.  Normally this is fine, but the Honda fuse holders tend to melt the ends of the fuse due to corroded contacts which makes heat, and thus melts the fuses ends.  Check them with an OHM meter to be sure, or just replace them with a new fuse.
Steve F

[Tintop]

+1 on doing more than a visual check of the fuses.  lost count of the number of times those glass fuses were blown at the end but looked OK on MGB's.

[Bodi]

First make sure the ground wire at the headlight connector is actually grounded to the frame. This is sometimes the culprit.
There's a bit of weirdness in some 76 bikes from Honda removing the headlight off switch, as daylight on headlight laws came in. Honda left the wiring harness unchanged for places that had no such law and installed a jumper for those that did, bypassing the nonexistent switch.
If you have a meter with test buzzer, switch the ignition off, connect one meter lead to the unplugged headlight connector (either high or low beam power terminal) and test to any unused bullet connectors (should be a male I think) at the main harness junction where the switchpods connect - switch from low to high beam each time or connect the meter lead to BOTH the low and high beam connector sections. If you get continuity then you have found the connector the headlight needs power to come from, you have to add a jumper to power it. I think it gets black ignition wire power here and that connector leads to the headlight fuse feed, I may well be wrong and you have to find the wire from the fuse's load side.
Otherwise, measure voltage at the HEAD fuse to make sure it's making it that far, should be at both ends of the fuse if the fuse is good. Remove the fuse and see which end is the power feed, the load side will not have voltage. Use the ohm meter or beeper to find which wire the load side is connected to at the fusebox connector. Find that wire at the switchpod harness junction and check continuity to the fuse. Make sure it's connected to the switchpod. Check continuity to the headlight high and low power wires from the switchpod while operating the switch. Check continuity through the harness to the bucket headlight power wires. If you have continuity from the fuse right to the headlight connector and power at the fuse feed... it just about has to work.

[rosh_thomas]

Hello folks,
I got a 1982 cb750 custom (one with a fairing.. its in my profile pic)...

Its weird that the headlight works fine in "P" - both low beam and high beams.
I think Ive got a busted fuse of some sort.

Any suggestions? My headlights dont work at all in "ON". The tail lights dont work in "ON" either. However, the brake lights work.

Looking forward to a reply!

Cheers