I don't know if this will help, but my 49 3100 has a horn relay mounted to the firewall. Atomarc is right about the 49 being a "crossover" year. Early 49's used up the last of the 48 parts. For instance, my truck has the later style 4 point cab mounting fastening system, but has the earlier stlye headliner "screw" in bow (?).
Which wiring harness did you get?
