Welcome to ALLFORDMUSTANGS!
Please read the Site Rules and be sure to complete your account details.
We’re glad you’ve joined us.
I would start with either the radio or the horn. Identify which fuse is supposed to protect that circuit.Then with a DMM, see if the fuse is is receiving power. If yes, then start checking the wiring that transports that power to that device. If no, then start checking the wiring that is supposed to bring power to that fuse. It sounds like you have missed a bad fuse somewhere, or a power lead got pulled loose.
Are you talking about an aftermarket alarm? Perhaps the alarm circuit has failed or came loose, and is preventing power from reaching the other items. You have start eliminating things. There is no shortcut.
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, builds, modifications, reviews, engine swaps, classifieds, troubleshooting, maintenance, and more!