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finding running light wire

Stone Blue

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I have a 1978 cb750k
i am trying to work out a tail light issue the brake light works fine but no running light i have a wiring diagram. my question is if the brown wire is for the tail light/running light. and according to the diagram it goes to the combination switch. where is this switch? thank you in advance!!!
 
Most prints refer to the combination switch ( labeled BATT. IGN. ) being the actual key switch, I,m confused as to why there is not a tail light wire under the seat? If there is take the headlight out and check all the connections most all branch circuits are in there.
 
Thank you. the brown wire i referred to is under the seat i checked for power and it has none. i will check connections behind the headlight tomorrow and will also check the ignition switch, which it might be that. when i turn the key to "p". the tail light comes on. that is the only light that functions.
 
P is the park position which will activate the tail light, I,ve had loose connections before inside the headlight bucket. since the Park light works I would eliminate the key switch.
 
i chased the brown wire to the ignition switch and its fine up until there. as you mentioned i checked the headlight bucket and found the same brown wire that split off from the same wire before the ignition switch but its not plugged into anything. i looked at my diagram and it shows no split like that. i guess i i have the wrong diagram. what should it plugged into?
 
Do You have 12vdc test light? If so with the headlight removed there should be connections with 2 into 2 or 2 into 1 there should be a vacant plug to use. With the test light check for power at these locations one by one with the lights on then verify that the power diminishes when the lights are turned off and use that location to plug the brown wire into, I do not have a print for Your bike or I could tell what color wire to look for.
 
CB750_K8_WD.jpg
I finally found a correct wiring diagram for my bike. it shows the brown wire going into the bucket is not connected to anything so i am leaning towards a bad ignition switch. now its doing something different.when the bike is running the tail light is on but pressing a brake makes no difference. When i switch it to park the tail light comes on and when i press either of the brakes the brake light comes on. before just the tail light would come on pressing a brake would not make the brake light switch on. (while in "p")
 
Had the same problem / found solution

I have a 1978 cb750k
i am trying to work out a tail light issue the brake light works fine but no running light i have a wiring diagram. my question is if the brown wire is for the tail light/running light. and according to the diagram it goes to the combination switch. where is this switch? thank you in advance!!!

I'm sure you've already resolved this bug considering it was posted in 2014. I came across the same issue on a newly bought project bike. Tail light works when the key is on parking mode but not when the bike is actually 'on' or running. So the problem, in my case, is actually located on the ignition but it's not the actual ignition that's at fault. Fold the rubber casing on the ignition backwards revealing the wires that are soldered to the ignition. (On the back of the ignition housing.) You will notice that the brown wire (tail light wire) has been split into two somewhere along the way from the tail light to the ignition. One of the wires engages when the key is on 'on' position and the other engages when the key is on 'park' position. In my case the solder broke for the wire that is suppose to communicate that the key is on thus the light did not work. Super easy to spot and fix. Solder it back on and DONE.
 
It's been a while since this thread was tapped into. I have a 76 CB750 SS that I've put a new/used harness in because the PO had modified a lot of the functions and clipped a bunch of wires. Tail light won't come on. The Brown tail light wire runs to the new ignition switch and there's 2 browns leaving the switch. They seem intact but I will reluctantly cut the factory plastic to make sure they are connected. The tail light will come on in park and the brake lights work. The speedo/tach lights come on with the turn signals, I think that will be a more logical fix. The tail light is baffling me. All the dash lights work/function but the neutral is always on. Turn signal lights aren't connected yet as I am waiting for my fleabay purchase to arrive. All the colors are connected correctly. I'm assuming the green wire is a common non-specific ground and it doesn't matter what green goes in there. There is a solid lime green wire that isn't shown as lime in the schematic, only one color solid medium green is shown. Thanks in advance for any advise.
Ray
 
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