For the money, it’s hard to beat this.
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Wire the positive wire to the orange power feed to the dome lamp. Wire the negitive wire of the LED to a pink ignition feed wire (or the radio power feed). It sounds strange to have power on both wires of the LED, but it will flash any time the ignition is off. Put the LED in one of the defroster ducts in the dash, make a thief question how bad they want to mess with the truck.
If the truck is carbureted with an electric fuel pump, put the kill switch on the power feed to the pump. That way, the truck will run probably 30 seconds, just long enough to get it out of the parking spot into the road. He would definitely think twice before sticking around in a stolen truck, stalled in traffic!!
The best cheap (free) idea I have heard is to swap the ignition coil wire and one spark plug wire on the distributor cap. Obviously this will only work on engines with a external mounted coil. The engine will crank normally, the engine might even attempt to start as the rotor aligns with the plug wire and coil wire (but will not run). Once again, a thief isn’t going to stick around with a stolen truck he just broke into trying to figure out why it won’t run.
Lock the doors, park in a well lighted area, the LED in the dash, and hope for the best. A determined thief will get your truck given enough time. If the can’t drive it away, they will tow it away, bypassing whatever security you have added. The best advice is to make it as difficult and time consuming as possible.