On 19/12/2015 23:44, JD wrote:
replying to Peter Andrews , JD wrote:
pa wrote:

Yes a fuse is essential, use an in line one close to your crocodile
clip, not that I approve of your method of connecting to the battery.
Without a fuse you run the risk of a few meters of glowing red hot
wire - been there and done it, albeit 50 years ago! Peter




I agree about the crocodile clip; I securely clamped the wire instead.
Surely, the bulb itself will act as a fuse, won't it? I couldn't find an
inline fuse today, so I wired it up with no fuse. Why would the wire get
red hot?
JD

A fuse is the 'weak link' in a circuit, it's purpose is to protect the
wiring in the event of a fault. For example, in your case, if you have
an accident and your headlamp assembly is badly damaged such that the
wiring is crushed against the body shell there is a real possibility
that the battery will supply as much current as it can down the damaged
wire which will result in it becoming very (red) hot and melting the
insulation and that of the adjoining cables ultimately catching fire.
The purpose of the fuse, located relatively close to the battery, is to
fail if an excessive amount of current flows therefore stopping further
current flowing and reducing the chance of fire. Please for your own
and your passengers safety fit a fuse, it's not funny being in a car
that catches fire it does very, very quickly become an inferno. Most car
fires are a total loss.

Peter