there is considerable liability incurred whenever you change anything from the original [safety and instructions to use, in the operator's manual] OEM placement, and when the operator hits a pedestrian while trying to blow the horn, from the OEM placement, where they were documented to have been trained how to blow the horn, will give the forklift operator a 'legal and legitimate' excuse, but will create a trail of paper that will lead right back to whomever wrote a work-order that said "install horn button" in some place other than the OEM location, with parts other than those as certifiable as 'at least as safe as the OEM'.
Please always be sure the repair you make meets "industry standards" and is at least as safe as the OEM repair that uses parts at least as safe as OEM parts.