2003 Ranger will have a PATS(passive anti-theft system) that will prevent starter motor and fuel system from working if the key used to start it isn't "recognized".
This system is as it says "passive" no horn or lights, just won't start.
Dealer, or past owner, has installed a perimeter alarm system, i.e. if something or someone bumps the truck or tries to break in the horn will sound and lights may flash.
Dealer installed are "factory alarms" but not installed at the factory, lol.
And these alarms usually only trigger if door is opened without unlocking it first, no motion detector.
3rd party usually include motion detection.
Can you turn the alarm on and off?
i.e. rolled down window, get out and lock doors with key fob
reach in and open door using inside handle and see if alarm activates
If not then you don't have an alarm and probably have a wiring/relay issue, horn circuit has power all the time, not sure if it is on the Battery Saver circuit or not.
Battery Saver cuts power to most fuses after truck is off for 20-30 minutes
Also does the horn work when you use steering wheel button?
On 2003 I think the horn relay is in "aux relay box 1" just above gas pedal towards center console, box has a removable black lid.
Google: ford ranger auxiliary relay box 1
Last edited by RonD; 01-10-2016 at 07:13 PM.