A wrench for tamper switch installation for use with a tamper switch arrangement including an enclosure containing a tamper switch assembly having a mounting rail for assembling the tamper switch assembly to a security system enclosure. The wrench may be capable of holding two separate nuts and have cooperating mating structure to slidably mate with the mounting rail of the tamper switch arrangement. The nuts may be frictionally-fitted into the wrench, after which the wrench is slidably moved onto the mounting rail until the nuts line up with two throughbores in the mounting rail. Two screws or bolts are then inserted through a surface of the security system enclosure and traverse the throughbores in the mounting rail. The screws or bolts then threadably engage the two nuts disposed within the wrench and are threaded therethrough via rotation with a suitable instrument, e.g., a screwdriver, located outside of the security system enclosure. The wrench prevents the two nuts from turning while an installer installs the two screws or bolts from outside the security system enclosure.