Sidelight bulbs blowing

[Bob Kneale]

'34 Tourer

6 volt positive earth

Dynamo giving about 7 amps on full, zero on half, charge - I assume the resistor has blown.

I will get round to fixing it soon.

The lights all work, at least, they did.   The headlights still work, but the side and tail light bulbs keep blowing.

The battery is supposed to regulate the voltage, isn't it, and why don't all the bulbs blow?

The head and side lights share an earth, and the rear light has a new earth straight to the battery.

Any ideas, anyone?

Thanks,

Simon

Dodgy bulbs- modern replacements most likely Chinese and often not long lasting. My 6 volt indicator  bulbs don't  seem to last

Cheers, Tony.

Hi Simon

Exactly the same happened to me 46 years ago when I first got my '37 Ruby on the road. Every bulb except the headlights blew, and I tracked it down to an intermittent connection to the battery (I recall it was the live i.e. the negative), which was going open circuit, causing the dynamo voltage to  rise excessively,  easily enough to fuse all the lower wattage lanps.
The battery regulates the voltage, by shunting the excess voltage to provide electric current to charge the cells. This is achieved by the fact that the battery has a very low internal resistance - the reason that lead acid and many other modern cells can deliver the enormous currents required to turn the starter motor (or cause fires in the event of a short circuit.
I solved the problem by making tighter connections to the battery - doing away with the 'helmet' connectors and fitting proper clamps, and the problem never occurred again.
Fortunately bulbs were very much cheaper then..................

Hope your problem is as simple as mine turned out to be! Moral - avoid potholes in the dark

Bob

Bodmin Cornwall - not far from Alastair