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Help with an electrical problem

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Shawzee

Shawzee

Joined
Nov 1, 2020
Messages
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Location
Christiana, TN
Hello again,
I have a 79 xs750 special, my headlight went out.. I check the light off the battery and ground and it's fine. Fuse is good. I searched around and learned that when starting the bike it doesn't allow the headlight to turn on until the engine is running so it doesn't draw juice from the battery. I took the switch apart and it looks clean, no wires broken, I took the headlight out and there are no loose connections in the bucket. I was considering running a wire from the battery to a fuse to a inline on/off switch. Are there any suggestions how to remedy this, someplace where I haven't checked????
Thanks in advance.
 
Typically a relay is used that passes power to the headlight once the starter button is pressed. I would find that and bypass it to confirm that the light is good.
 
Shawzee said:
....someplace where I haven't checked????
Click to expand...
There is a latching relay that closes and stays closed after the engine starts. My Kaw had that.
If you have or can find a wiring diagram it should show it and the approx location.
 
ZRX Mitch said:
Typically a relay is used that passes power to the headlight once the starter button is pressed. I would find that and bypass it to confirm that the light is good.
Click to expand...
Said well, but I see it bypasses power to headlight and directs it to the starter, when starter button is depressed. Then once starter button is released power returns to headlight. We are saying the same thing I think :). In my trade we have the same principle on starting some high ampere HVAC equipment for various reasons.
That is a good call Mitch, I bet you are correct.
 
It's probably the relay. But it may be the supply wires for the relay, may be a wire with insulation worn through shorting to the frame or a bolt head somewhere preventing the relay from firing, broken wire from fatigue in the harness, corrosion under the insulation due to 43 years of water ingress, etc., all of which have precisely the same symptoms as "bad relay", which may cause you to replace the relay and then rule out the whole circuit when "that didn't fix it".

The reality with electrical stuff on motorcycles is that you are going to have to break out the multimeter and begin chasing wires and testing the circuit while following the wiring diagram. Ultimately this will be quicker, easier, and more effective than just trying to replace parts and hoping to get lucky. You can easily test that relay and rule it out as the cause, but then you have to test the wires and find the actual problem.
 
Nah.
Just think of wires as pipes that carry smoke.
Pressure is voltage. Flowrate is current.
If the smoke comes out, things stop working.
 
mr72 said:
It's probably the relay. But it may be the supply wires for the relay, may be a wire with insulation worn through shorting to the frame or a bolt head somewhere preventing the relay from firing, broken wire from fatigue in the harness, corrosion under the insulation due to 43 years of water ingress, etc., all of which have precisely the same symptoms as "bad relay", which may cause you to replace the relay and then rule out the whole circuit when "that didn't fix it".

The reality with electrical stuff on motorcycles is that you are going to have to break out the multimeter and begin chasing wires and testing the circuit while following the wiring diagram. Ultimately this will be quicker, easier, and more effective than just trying to replace parts and hoping to get lucky. You can easily test that relay and rule it out as the cause, but then you have to test the wires and find the actual problem.
Click to expand...
Yes you are correct. It could be not getting 12VDC to the relay coil or points inside the relay bad. Wouldn't you say it is a DPNONC or maybe just a SPNC ? I can read wiring schematics and diagrams but usually use the locate and trace method :mrgreen:
 
A Honda I had came with a faulty switch , several sets of contacts inside the switch for exactly the reasons you have above required it to be made with so small of contacts that it was simply a *** . Mine was the starting circuit so I added a hidden starter button that would allow me to start the bike anytime I wanted . If you add a headlight switch just make sure its not direct to the battery but powered from a switched source . That was the reason I added my own button , I didn’t want to spend over a hundred bucks for another faulty factory *** switch .
 
I'm mystified what word was replaced with "*** above. Either you really, really hated that switch and use creative profanity to describe it, or the profanity filter caught up a regular word, kind of like on another forum I am on which often has references to a "pet chicken" used as a fuel valve.
 
Cagiva 549 said:
A Honda I had came with a faulty switch , several sets of contacts inside the switch for exactly the reasons you have above required it to be made with so small of contacts that it was simply a *** . Mine was the starting circuit so I added a hidden starter button that would allow me to start the bike anytime I wanted . If you add a headlight switch just make sure its not direct to the battery but powered from a switched source . That was the reason I added my own button , I didn’t want to spend over a hundred bucks for another faulty factory *** switch .
Click to expand...
I want to add a headlight switch on my Honda XR650L for off road riding at slow speed where it charges battery better. It will also help if I need to run from the law at night and I won't use the brakes. I still back my scooters into a parking spot for a quick getaway even at age 72 :rofl:
 
I removed the reserve lighting unit, cut the blue/yellow wire and connected it directly to the other connector blue/yellow wire and I now have a headlight as soon as I turn the key. Thanks for all your help.
 
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