Rear Bulbs blowing on Primmy 125

[Spud]

Got a problem where both the rear bulbs keep blowing on Primavera 125.
Front headlight is OK & speedo bulb is fine.
I even put a 15w bulb in to try & get home & fried that in a couple of minutes.
Could this be a bad earth or what else can i check?
I have a multimeter, so i can take some readings if i new what i was looking for!

[mickymidas]

Festoon bulb ?...Could be as simple as vibration ....my rally did the same with old festoon bulb fitting , cured it by wrapping elastic band around terminals ...took vibration out and kept terminals tight fitting....lasted 2 years

[jonny snatchsniffer]

most likely a bad earth, or stator coils breaking down, you havent mentioned the pilot light as that is still on with the main lights, try some 12v bulbs if the earths are fine and if it blows them then its rewind or upgrade of ignition and lights
a zenner diode fitted between the live to the light and earth will limit the voltage

[Spud]

Checked the earth & is fine!
When the brake pedal I pressed, the rear light goes off.
Blows 12v bulbs when revved!
Can I just fit a Zener diode in line with the bulb & if so, how are these rated?
Cheers
Spud

[firekdp]

When the brake pedal I pressed, the rear light goes off.

This will happen, if the brake light lamp is blown/not connected properly.

Is there a pilot light fitted, has this blown?? The speedo is also on the same circuit so it's strange that this isn't blowing as well.
Make sure ALL lamps are the correct voltage/wattage and are in good order or it will unbalance the system.