Hello, I just bought a Ford f150 and when I opened the hood I noticed it had an aftermarket horn. But, the horn doesn’t work. I did some troubleshooting and realized that when I do a continuity test from ground to the 12v wire supplying the horn, I read continuity. I know absolutely nothing about horns, but the after market horn has a 12v prong and a ground prong on the actual horns that you have to connect your wires to. If I put my meter on those 2 prongs (ground and hot), I read continuity (meaning they are touching), which is obviously not good!
I can’t even open it up to fix the problem, the little thing is just one piece and can’t be opened. Am I completely screwed and have to buy an entire new horn because of this problem 
Anyone run into this same problem?! Thank you for your time and help
Post some pics so we can help you.
-Kris
Alright will do, let me wait until tomorrow morning to get better pictures for you.
Quite the contrary. If the horns are air driven, what you’re probably testing is a solenoid. It’s basically a coil which creates electro-magnetic force to actuate an air valve. A coil obviously has continuity. Put 12v to one side, ground to the other and listen for an audible click. The other aspect you can test is 12V power on that supply wire. Of course you only want power on that line when you want to blow the horn, which would be controlled via a switch (e.g. steering wheel horn button or another temporary switch).