With the horn, it could be a bunch of different things, from the horn button, to the contact from the steering column to the steering wheel, to the horn itself. With the interior lights, are you talking about the dome light or the dash lights? I know my dash lights had a bit of corrosion where they contacted the circuit board, and also, my headlight switch was bad and didn't route power to that circuit
Oh, the red horse is your high beam indicator light