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I keep blowing the fuse for my lights on my CB750.

I put on new turn signals and tail light.

Why does a fuse blow?

If my headlight is not on the bike right now, is it possible that the problem could be not enough grounding? In other words, do i need the two gounds in the headlight hooked up in order to properly gound the lighting system?

Thanks
 

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the fuse holders on cb750s are notoriously bad designed. They corrode on the back and when that happens sometimes the corrosion touches the other electrodes. This heats up the plastic case and the fuse electrodes begin to gravitate toward each other. Once they get loos enough to touch they begin to pop fuses starting with either the main fuse or the lights.

Pull off the fuse cover and have a good look, wiggle the fuse holders around and if they seem loose then replace the whole fuse box. It is a common fix to replace the fuse box with blade style female connectors and use standard automotive blade fuses in place of the old glass tubes.
 

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Also make sure your battery is not moving around in it's holder. Sometimes the positive lead can bump into the frame and short all kinds of stuff down the line.
 

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i have one of those cheap repro lucas tailights. the running light doesnt work anymore in it. and i cant get the brake light to activate anymore. there is a wir that runs under the seat that goes along the top of the fender, with a connector. if you are of large stature (ie, fat) or ride around fat chicks alot, its possible thats been smashed into the metal fender and causing a short. my bike will now randomly blow the main fuse, im certain it has to do with the taillight.

jc
 

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well for starters, glass type fuses aren't really even suitable for guitar amps

much less any sort of vehicle

this is why you cannot buy a vehicle made after say..... the mid 80's that has them anymore
 

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Fuses blow because there is either too much draw on the circuit or there is a short to ground. Check the rating of the fuse in your manual for the cb750. If the fuse is blowing as soon as you turn on something - then it's more than likely an overdraw thru the circuit (like a short or wrong wire hookup). If it takes a while for the fuse to blow - then the fuse is under rated for the circuit. If the new lights require more current thru the circuit - then your fuse is likely undersized.
 

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more than one glass fuse has "blown" in the soldered ends and appeared unblown

because of impact or it being subjected to the first harmonic

now to methodically diagnose which of your five newly installed lights is causing your problem

disconnect and reconnect them one by one until the fuse stops blowing

then trace that circuit and usually a good visual inspection, in such cases, will reveal the problem

which will likely be an error you made installing the lights or even an error inside the lights themselves
 
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