Wiring up car alarm for nissan pulsar n15 1999

First thing I see is Pulsar last year being made was 1989.

No mention of which model of alarm you are going to install???
so heres some sets to concider,,,,,

That makes it interesting.lol

sounds like the wiring loom is transposed,
wiring around the wrong way.

Go to each of the motors that drive the central locking,
visually site the colours and where they are connected ,
get a multimeter and test the output from alarm to each of the motors ,
Arm/disarm each motor as you remove each cover.
this will elliminate each area and rule out as a possible fault,

Have you changed the battery on your remotes lately???

Hope this helps....