Lexus alarm 1996 lexus GS300 alarm won' t stop unless battery is disconnected

My GS 300 arlarm kept going off now for two months unless the battery is disconnected; the solution to my problem was that my key had an electrical fault. I confirmed it by placing the faulty key within a metal box or a steal pot with a heavy lid. upon doing so it stopped going off. I later purchased a new key

There is an anti-theft relay that is stuck open. that needs to be replaced. I'm unsure of the location, probably under the dash somewhere. it will be a small, plastic box about the size of a pack of cigarettes.