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Author Topic: '78 cb750k running light gremlin or "Where does this other brown wire go?"  (Read 715 times)

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Offline Kev Nemo

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'78 cb750k running light gremlin or "Where does this other brown wire go?"
« on: June 10, 2009, 08:59:07 PM »
So I switched out my stock tail light for a smaller unit a year ago and I've had problems with the running light going popping but the brake light working fine. I undid the wiring harness and traced the brown wire up to where it splits-one goes to key assembly, the other is cut off.

I don't have turn signals in the front or back, so the only wires coming from the back are the green/yellow, brown, and ground.
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Offline Sporkfly

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Re: '78 cb750k running light gremlin or "Where does this other brown wire go?"
« Reply #1 on: June 10, 2009, 09:16:01 PM »
Just a shot in the dark here... Does the brake light work by the hydraulic switch for the front brake?
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Offline TwoTired

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Re: '78 cb750k running light gremlin or "Where does this other brown wire go?"
« Reply #2 on: June 10, 2009, 10:44:21 PM »
If you haven't looked at the Honda shop manual 78 750K wire diagram (pg 279) yet, you'll find it is normal to have an unconnected brown wire up front for the US model bikes.
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Kev Nemo

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Re: '78 cb750k running light gremlin or "Where does this other brown wire go?"
« Reply #3 on: June 11, 2009, 06:59:33 AM »
TwoTired-I did look at my Clymers manual but I guess I was too tired at the time; I'm sure you're familiar with the feeling. ;D
Any ideas on what could be causing the short? I'm thinking it could be the ground wire that runs from battery neg terminal to the actual light housing. I'm not a fan of having the ground just screwed in the an eyelit as it is now.
Would it be safe to snip the wire at the solder just to clean up the spot? 

Sporkfly-Yes, but it also works with the rear pedal as well. The running filament is shot and the brake filament is fine.
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- '78 CB750k bobtrack

Offline TwoTired

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Re: '78 cb750k running light gremlin or "Where does this other brown wire go?"
« Reply #4 on: June 11, 2009, 12:13:39 PM »
Is your replacement tail light vibration isolated like the stock unit?    The filaments get softer when they are lit.  The stop light is intermittently on.  But, the run light is on for a far longer duration, making it more vulnerable to shock damage.

You can't burn out a filament without it getting more voltage than specified.  What is your system voltage?  I see no wiring faults that could cause it to fail from over voltage/over current.  The battery can't do it on it's own.  The charging system won't selective prey on the tail run filament only.

I expect you have a vibration problem.
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Kev Nemo

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Re: '78 cb750k running light gremlin or "Where does this other brown wire go?"
« Reply #5 on: June 11, 2009, 09:28:57 PM »
I found a loose black wire that I jumped up to the brown wire coming from the ignition switch (which I also cleaned). This solved the issue.
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