help please

hi all new here
my dads got a p38 i think, its a 97 4.6 hse had it three weeks and battery flat, got a new one and now thats flat.
read on here about the rf draining the battery so i disconnected the wire and then it wont start it says engine something on the dash so i put the eka code in and then it starts but next time i try it doesnt i have to do code again :doh: why is this, help much appreciated thanks Andy.

dunno, depends on which wire you yanked? for example, you only need to disconnect the antenna to the RF receiver, not the whole receiver.