Backman - while I agree that going and getting an entire system is the best option, a properly wired (proper tinned & guage, soldered, e-greased, shrink tube) float to horn is an acceptable solution and significantly better than not having any solution at all. Now if your horn is failing all the time don't you think you should have upgraded to a better solution? You do check your horn frequently enough to confirm its working?
I checklist my boat all the time, full systems check, bilges operations, float swiches, debri, hown, lights, etc. And now adding the Thru-hull to that...
On that throughhull - I'd be removing, rebedding, and replacing that before I ventured out again. If you can turn it by hand it is either leaking or ready to leak.
And yes, I am completely redoing the thruhull, one diameter larger, glassed in new backing block, regoop, etc... One of many current upgrades/repairs going on with the boat...