Battery drains when cold outside

I had fuel pump replaced.  Then car started having
problems holding a charge doesn't work then the
mechanic ran a wire from the fuel pump to the
circuit box in the engine and told me that when the
car wouldn't start and I needed to hit the wire
against the metal in the circuit box well I haven't
had any more problems until it got cold and then
every night that it's cold the battery drains so I have
to jump start it that wire is just wrapped around the
circuit box it's not I haven't had to use it but every
time it gets cold the battery drains what's causing
it and what do I need to do