Is there power at the horn connector when the horn switch is pushed?

 

My horn stopped working one time, both of them (low tone and high tone). And I thought the worst - electrical issues. Turns out, it was an easy one. The power runs into the one horn and jumps to the other. The wire going into the first horn broke due to corrosion. Re-spliced the wires and all is well.

 

Not trying to be snide but did you check the test light on a known good source of power to make sure it actually works ok? If so, then you are correct that the problem is upstream of the fuse/relay block...but that would mean a lot of other things wouldn't be working either so it's not likely. Make sure your test is actually correct before chasing a wrong diagnosis. I'll check my wiring diagram tomorrow but it's for 2007.

 

This is from the 2007 FSM not sure if the same for 2013 but the concepts are the same. Where exactly did you place the test light terminals? Not sure what kind kind of test light you are using but I would place one terminal on battery ground and one terminal on battery positive to ensure the light works ok. Then leave one terminal on battery ground and then other terminal on pin 3 of the horn relay and then pin 1. You should see the light on for both. If no light go back to the fuse and leave one light terminal on battery ground and the other terminal on both metal test points of the fuse. Light should come on for both metal test points.

Is this what you did? Be aware that not all grounds are created equal. I always begin tests using the actual ground terminal on the battery (use an extension wire if necessary) and then once that test is ok you can move to local grounds which can help you find if your problem is from the ground side or the power side.