i find it hard to believe that a relay would be causing the problem. however, did this problem occur after the alarm system was installed? if so, take it back to the installer.
there may be a short somewhere. normally, aftermarket alarm system relays are located under the dash. try pulling the fuse for the alarm system and see if that does, in fact, drain the battery. if the battery is still dead, then it's another issue. pulling fuses may help in diagnosing the problem, tho it may take a while because you have to pull one fuse at a time and wait for results. a voltage meter comes in handy for this.
electrical issues are hard to diagnose on-line. so, again, did this problem happen after the alarm system was installed or before?
when i need to work under the dash for a long time, i find it easier just to remove the seat(s)...i'm not that tall, but at my age i'm not as agile as i used to be....lol
