CB125 Rear End Problem

[Jenkosowls]

Hi my CB Keeps on blowing the rear end bulb but not the brake light. Any 1 know what it could be and would having an LED Bulb Stop this or would it blow an expensive LED Bulb

[stinkwheel]

What sort of CB125?

A Honda one?
Single or twin cylinder?
Year of manufacture?

I ask because there are important differences in the electrical systems.

Could be caused by voltage fluctuation, excessive voltage, an intermittant contact or simple vibration (the light filament is thinner than the brake and breaks more easily).

So, make sure the bulb holder is free from corrosion, the bulb is a good fit and that the connectors leading to the holder are well attached. An old trick to eliminate vibration as a cause is to take the lamp unit off and refit it with a piece of rubber (old inner tube) behind it.

[Jenkosowls]

Hi yeah it is a honda Single 1985 i dont think its a vibration problem as the mounting is rubber it self

[hmmmnz]

the only thing that really causes a bulb to blow (apart from shit quality) is over voltage or vibrations
check the voltage and get a good quality bulb
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[stinkwheel]

It probably has direct lighting (head and tail light runs on AC power direct from the alternator). Do you use the daylight running light a lot rather than the full headlamp?

If it is direct lighting, there will be a ballast resistor located between the forks, under the headlamp. It's about four inches long, cylindrical and has lots of fine wire wrapped round it. It has one wire going to it (usually pink). Check this wire is attached and that there isn't a load of rust under where it attaches to the frame. This resistor 'balances' the power draw when you are using the daylight running light, if it was disconnected, the taillight would be fed too much power.
https://www.cdxetextbook.com/images/350px-Ballastresistor.jpg

Also, if the speedo backlight bulb is blown, replace it.

Vibration wise, it isn't so much the presence of vibration because there is always some, it is the frequency of the vibration, adding or removing rubber backing alters the frequency to one that shouldn't break the bulb filament.

[MattHirst]

Are you getting replacement bulbs from halfords (standard 21/5 bulbs?).....if so then don't.

I kept doing this until someone said get a proper one from a bike shop, as aparently they have a third 'prong' that is a vibration damp.

I kept getting the ones from halfords, and blew one roughly every 1/2 weeks, but now i have this 'proper' bulb then i haven't had one blow, for about 2 months now.

[Jenkosowls]

Hi all thanks for the advice iv maaged to fix the problem with handy Voltage regulating chips seems to do the trick