As subject says, my 1998 civic 1.4 wont start when its been below freezing outside.

I can use the car fine for days without problems, but when its cold outside I come out at morning only to find a dead battery.
(I measure about 10V at the battery)

Changed the battery. Problem remains.

Charging voltage is ok (14.5V).

Something is draining my battery, but only when cold. Any ideas?

 

You may be able to pinpoint the parasitic battery drain by disconnecting various electrical components and determining which one stops the problem. Start with components independent of turning the ignition key ON.

 

I just noticed that my stereo amp (its a 10 year old junk amp) is operational even with the headunit off.
I measured voltage at the remote lead and there was no voltage there.
So I disconnected the fuse to the amp and hooked up an current-meter accross it. Turns out the amplifier draws 1.2 ampheres with the ignition off.

I think I've located - as you put it - the paracite.