Exactly, the short is below the heat required to blow the fuse link but can start a fire. An amp gauge in series between the fuse link and the starter relay post would be the starting point. The horn and brake lights is always hot and a soft short in a turn signal or the horn, likely the horn would overheat the off shore plastic turn signal assembly. Carefully manipulate each wire to those circuits while an assistant stares at the amp meter and if the draw goes away for a second the assistant yells, stop and you don't move your hands and stare at what do moved. A D-Arsonval meter is best used for this as the digital tend to flash and is not as clear to see as a needle drop. Good luck