[Bill G]

As was mentioned in two of the previous posts, the electrical path both within the horn and external connections needs to be considered. Don't overlook the fact that the horn button itself is part of the electrical path. It is an electrical switch. Its contacts after 90 years may be dirty or pitted. The electrical path of the horn first has a yellow wire that connects directly to the generator [or alternator], and that wire is always hot. The blue/yellow wire is the path to ground which goes through the horn button on its way to ground. If you take a jumper wire and go from the blue/yellow wire contact on the horn to ground and it should blow the horn. If it blows better by using the jumper than the horn button, then that tells you that the horn button may be your problem.