You have that the wrong way round Baz - the resistance of the bulb is the constant, it's the voltage that's the variable. As voltage increases and the resistance stays the same the current increases. Therefore higher engine speeds = higher voltage = higher current. always allow for this in calculating wire ratings. In the aircraft industry we used to do that, add 50 per cent then double it :)

Well, that's close to multiplying by pi, which is used when estimating software development ;-D

i worked out the rating then doubled it on everything.

doh i know. i was just thinking in the wrong wavelength again
its the night shifts you know :(

here's a quick calc linkey so no thinking is required :rolleyes:

http://www.sengpielaudio.com/calculator-ohm.htm

55w bulb = 2.61 ohm at 12v

11.5v=4.41A
12v=4.58A
14v=5.34A