Need help with strange horn problem

[ScottH]

Problem is I cant get it to work, it is a 72 c10 with a grant wheel. When I press on the horn button the horn relay clicks like it should. If I use a circuit tester on the horn wire it lights up when I press the horn button. I have tried 4 other horns plus a brand new one and none work. Cleaned all grounds, even tried hooking each horn directly to the battery and none worked. Also replaced the horn relay with a new one, same results.

If anyone has any suggestions on what to do next I would appreciate it.

Thanks
Scott