1.6 gti electrical problems

i have a 205 1.6 gti on a J plate and when i bought it it had a knackered engine, i managed to get hold of anouther engine, but out of a E reg. i was told it would drop straight and run off the same loom ECU etc that the J reg one did. now ive got it all fitted im having loads of problems:

no gauges work on dash
fuel pump runs sometimes after ignition is turned off
when battery is low car turns over slowly and rev gauge moves
car doesnt start very easy when cold
battery light is on but alternator is working

thats the main ones. if anyone could help i be very grateful