1142-18SMD-BA15D LED bulb

These LED bulbs are the brightest available, featuring the latest technology allowing them to run on any voltage between 8v and 30v. It uses 18 Surface mounted high power LEDs 
Note: They have a built in voltage regulator, the 12v only versions are cheaper however they do not last as long as the voltage fluctuations can shorten the life of the LED. 
These carry a 2 year warranty

These are a direct fit for your old bulb with 2 contacts and parallel pins. Specs:
360 degree -visible for miles 
Electronic current limiting - 8-30 V DC - bi-polarity
Dual contact (positive and negative on the base) BA15D
Parallel pins
Will work on 12v and 24v systems
Power consumption: 2.4w
Warranty: 2 years 
330 Lumen

Note the new version is slightly smaller than the picture as it has been upgraded.

Colour: cool white or warm white.

Length: 45 mm
Protrusion out of socket: 25mm
Diameter on top: 20 mm