1981 Honda CB 750C electrical issue

woodsman said:

Bad/corroded connections.

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DillonDeland said:

Oi, I am new to the community and am restoring my first bike. Having an issue and could use some input. Went to see if the bike would turn over and it did but the headlamp doesn't work now and no power to tail lights either. Horn works though. Where would you start? Voltage regulator or stator? Thanks

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TrialsRider said:

Do you own and know how to use a multi-meter, have the electrical schematic diagram and service manual and know how to read it all or need any assistance with that part? Because electrical trouble-shooting motorcycles all starts there. and yes you would start from the source, so that would be you stator output. OEM service manual makes it super easy and It's all interesting fun stuff, if it's not cutting into your riding season.

Horn does draw a lot of power so that is an indication that at least that has a decent ground and battery feed. With a meter or even better an oscilloscope you could literally put a value on how good every part or assembly is working.

Restoring it cool ! will be very expensive if you need to replace the 4-pipe exhaust.

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TrialsRider said:

Do you own and know how to use a multi-meter, have the electrical schematic diagram and service manual and know how to read it all or need any assistance with that part? Because electrical trouble-shooting motorcycles all starts there. and yes you would start from the source, so that would be you stator output. OEM service manual makes it super easy and It's all interesting fun stuff, if it's not cutting into your riding season.

Horn does draw a lot of power so that is an indication that at least that has a decent ground and battery feed. With a meter or even better an oscilloscope you could literally put a value on how good every part or assembly is working.

Restoring it cool ! will be very expensive if you need to replace the 4-pipe exhaust.

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oldhondacafe said:

Hi, I have a 1980 CB750c, for about 8 years now, when I got it. It had sat out for over 4 years and had similar issues. The fuses would be a good start to check, also wiggle them in the holder or run some scotch bright pad through the fuse holders and fuse ends if you find any corrosion. I found that several of the connectors had corrosion and wiggling them caused the light to come on. I found a battery cleaner/ protector (in spray can) that cleans the green corrosion off the connector without to much work, I think it was "Permatex", it cleans chemically and you can leave it on after, that's how I did it and It's been fine for years .The other place that causes this problem would be the light switch itself. You can disassemble it and clean those contacts inside it. corrosion is often the problem on 40 + old machines. I have a Suzuki that had head light issues, and the switch was melted and I had to replace it. This old Honda is probably my favorite old bike to ride, it's reliable, comfortable and does every thing I need it to do. I hope you can get yours sorted out too.

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TrialsRider said:

Wait 1981 thats a twin cam, thats not even old! the exhaust won't be horrendous expensive.. lol

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TrialsRider said:

Wait 1981 thats a twin cam, thats not even old! the exhaust won't be horrendous expensive.. lol

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TrialsRider said:

Wait 1981 thats a twin cam, thats not even old! the exhaust won't be horrendous expensive.. lol

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Geeto67 said:

Did you check the lighting fuse?

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8ball said:

Voltage regulator and the stator only come into play when the bike is RUNNING. All they do is charge the battery. If you have electrical issues when the engine isn’t running, it will be fuses, connections, wiring, etc.

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DillonDeland said:

...
Good point, glad I read your post tonight, was just looking at a stator/regulator combo. I may still replace it at some point but I will check what you suggested before I throw parts at it. Thanks again.

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TrialsRider said:

You might replace the regulator with something different, but you won't be changing the stator with anything other then another one the same :| that's what the meter is for, you need to measure the stator outputs first, thats where the power is generated. there will likely be 3 of them all same colour.

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woodsman said:

Are you sure your battery is good? If things aren't lighting up when the key is on then it will be battery, bad contacts/wire, fuses or the switch. Don't look past where the problem could be, the charging system isn't why it won't start. Get a meter and see where the current stops.

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