Charging system

Hello, I have an issue with the charging system on my 79 kz750 twin . Basically my lights get really dim after a few minutes of running the engine until it cuts off . It will run great hooked up to a charger and will run for a good amount of time if I run it fully charged but I shouldnt have to hook it to the charger every other ride like some electric bike . What goes bad in the charging system that I need to address , not sure where to start . -Shmeck

Schmeck wrote: Hello, I have an issue with the charging system on my 79 kz750 twin . Basically my lights get really dim after a few minutes of running the engine until it cuts off . It will run great hooked up to a charger and will run for a good amount of time if I run it fully charged but I shouldnt have to hook it to the charger every other ride like some electric bike . What goes bad in the charging system that I need to address , not sure where to start . -Shmeck

Would first assure good ground of the black wire from the regulator, which connects to a black/yellow wire going to battery negative.

Good Fortune!

it seems to be grounded pretty good . What should i be reading from my battery . When it was running I had around 17 volts and reving it up it jumps between 19 and 20 on my meter . Is this high or low ?

I just had the same issue on my GPZ street bike the regulator/rectifier was dead.. changed it last week.

Mine is about 14 volts when idleing, and does not move when revved. 17 seems awfully high at idle. Im going to go with regulator also.

Don't replace anything just yet.
You have dim lights, and the battery is dieing on you but you have 17+ volts at the battery?
If the Battery is old, or bad, get a new one first. If you have 17 volts accross the battery, then you should have 17 volts running through your lights and Ignition. Then they would be really bright, and most likely blow the bulbs at least. But with things dim, and a battery not charging, sounds like you have a wiring issue, maybe a bad battery also.
Use your wiring diagram to make sure of the connections from the battery to the regulator/ rectifier assy. If yours is a 6 wire R/R, what is the voltage at the Brown wire compared to the battery voltage at key on? Less than .5v difference? If it sees a drop here, on the voltage sensing wire to the R/R it will make up that difference and overcharge. With a big voltage drop in your electrical, you will experience the dim light condition also. Start with the basics, and test with a meter to find the wiring problem first, and get the battery checked and replace it if needed. You need a good battery for the system to work correctly.

Those readings were with the bike running with only running light at rear . After a few rides or long ride the battery will wine down and eventually become dim . This low voltage makes the bike run slow and ruin the spark plugs. Yes my lights are extremely bright which will hopefully keep people from making an eraser out of me Battery was brand new about a month or two ago . Had it replaced when I was taking everything apart . Heres a question bugging me . On the white regulator connector there are two yellow wires and one black wire in the connector . Now coming out of the Harness or side is only two yellow wires . No third black wire . Hard to believe that there isnt a black to black wired connection here .

Okay so I turned all my lights on and tested the battery and I am getting 14-15v at idle and 17-18 at high rev which Is alot lower . I switched out the black wire connector with a better one and will see if that was the issue