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1979 Honda CX500
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3 Posts
Discussion Starter #1
Hey guys, new owner and first time poster. Happy to be here! 馃檶馃徑

I bought this 1979 CX500 a few weeks ago and the owner mentioned the low and high beams weren't working. He briefly explained something wasn't connected and I thought it would be pretty straightforward once I opened it up but I still can't figure it out.

The halo ring works but I can't get the low and high beams to turn on. Any ideas of where I can start to look at to fix the issue?

Thanks in advance! Any help would be appreciated 馃檹
205632
 

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You will need to find the wiring diagram for that light so that you can determine where to connect to the bike wiring harness.
 

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CX500EC Eurosport 1982
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15 Posts
I have found that high and low beam terminals are inconsistently wired so you may need to swap them around, however the light should still work in these cases. First I would check that there is voltage getting through to the high and low terminals and that this is responding to the switch input. If that鈥檚 ok then you have a ground connection issue.
 

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I have LED bulbs in all 3 bikes, simple H4 plug and play. I second what Randall says.

Heck, could be a bad High/Low switch too.
 

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I am just a parts guy but before I would call my neighborhood expert Randall I would made sure the lite I was given was good if it is then I would borrow working stock lite & with stock wiring diagram get that lite to work. If it all works stock then should work with your LED.as Joe mentioned. If your stock lite doesn't work then start checking connections-switch-etc.
Paul
 

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I am just a parts guy but before I would call my neighborhood expert Randall I would made sure the lite I was given was good if it is then I would borrow working stock lite & with stock wiring diagram get that lite to work. If it all works stock then should work with your LED.as Joe mentioned. If your stock lite doesn't work then start checking connections-switch-etc.
Paul
I am assuming it never worked for PO-not just quit.
 

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Some bikes (including the '79 CX500C) have tail light warning devices and similar that can cause problems if you change to LED tail lights without removing or bypassing said device. The only ones I know of with something like that for the headlight are '75-'77 GoldWings, which have Reserve Lighting Units that work with both headlight and tail light but they were so unreliable that bypassing the RLU was recommended practice long before LED vehicle lighting...

I'd start with unplugging the headlight from the bike and measuring the connector too. The green wire is ground (common to all circuits in the bike and connected to the battery's negative) so connect your voltmeter's black test lead to it and check for voltage at the white wire (should be live when the switch is set to low beam) and blue wire (should be live when the switch is set to high beam).

If you don't have voltage there check the fuses under the cover in the middle of the handlebars. And don't trust just looking at them because years of vibration can cause the link of a glass cartridge fuse to break next to where it is welded to the inside of the cap so pull the fuses and test them with an ohmmeter (should read the same as when you touch the test leads together.

When these bikes were made it was standard to connect the common terminal of a headlight to ground and switch the positive between the high beam and low beam filaments. As car headlight switches became more complicated some designers found it easier to connect the common to positive and switch which filament was connected to ground. This was OK for incandescent lights because they don't care which direction the current flows through them but an LED headlight needs to have the current flow in the correct direction so if your headlight was intended for use in cars that have the negative switched it won't work on a bike that has the positive switched.
As I was finishing typing that I remembered that the "halo" works and I can't see a separate ground wire for that in your picture. I would expect that if the halo part uses the same ground as the rest of the headlight and it works this is probably not your problem but I'll leave it there in case it helps someone else who finds the thread.
 

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BTW: Welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided lines.
 

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1979 Honda CX500
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3 Posts
Discussion Starter #14
Thank you for all the input and feedback everyone! I will take more time trying to figure out the issue and will keep these comments in mind. I will update you with more info.

Thanks also for the welcome. I truly am happy to be here and I look in awe at that beauty of a '79 whenever I pass her. Looking forward to taking care of her for the years and decades to come.
 
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