In planing to bring the 83 D-150 into the 21'st century, I added power door locks,, thinking that some other lost sole may prize this truck as much as me, I also added an alarm.

It was a ez install, got the complete kit from A1 Electronics / Torence CA
www.a1electronics.com

Got a MES central door locking kit and an Avital 3100 security system (same folks that do the Viper Car Alarms) for 128.20 shipped,,

My truck is a two door, but the alarm system is 4 door / trunk / valet parking compatable, has a flashing led dash light when armed, includes a loud siren.
Being integrated with the power door locks, has a key fob,, press a button on the key fob, the doors lock, alarm sets, dash led blinks... return to the vehicle, press the key fob button, doors un lock, alarm dis-arms..

with just a bit of wiring intuition the install instructions are easy to follow,,,pretty cool for under 130.00,,,

To each their own, if it works for you then great. I often see aftermarket alarms start going wacky after several years time- I rip them out of customer's cars on a regular basis.

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63 Valiant Wagon
225 - 4 bbl