I have a diesel 3/4 ton truck, a Ford F-250. The previous owner had an anti-theft and alarm system installed on it after he purchased it. The anti-theft system began giving me trouble, and at one point, I had to disconnect the alarm in the middle of the Wal-Mart parking lot, because it wouldn't stop making racket.
Then one day the truck refused to start. You could turn on the ignition, and the glow plugs would cycle on, and everything would work, but you couldn't get the engine to crank. I hoped maybe it was just the ignition switch, and so I replaced that.
I bought this:
It's a little relay and pushbutton to operate your starter solenoid. Link to product
Installation took a couple of hours and wasn't difficult. It did require soldering to add length to the wires and insulating the solder joints, as well as crimping on some wire lugs. Those tools and skills are probably not mentioned in the directions. Still it turned out very well and works like a champ!
Below: I found a place on the instrument cluster that had no wiring behind it. Drilled a hole and mounted the button.
The button wires pass through the firewall, and plug into the relay. I mounted the relay to the firewall. The black and red wires energize the relay when the button is pushed. I connected the black wire to ground, and the red wire to the windshield wiper circuit. This prevents the engine from being able to crank unless the key switch is in the ON position.
In the above photo, the two blue wires are the ones that get connected when the relay energizes. They weren't long enough to reach the starter solenoid, so I soldered an extra 7ft of black 18 gauge wire to them, then insulated the solder joints with heat-shrink.
Below, where the blue relay wires (with black 7ft extensions) ended up, on the starter solenoid. The lower lug connects directly from the battery positive post. The upper lug energizes the starter solenoid.
So if you are following, turn on the ignition key and allow the glow plugs pre-heat the cylinders. This also energizes the windshield wiper circuit, where the new start relay gets power from. Press the start button, energizing the new relay. The relay makes a connection from battery positive to the starter solenoid, activating it. Full battery voltage is applied to the starter, which cranks the engine. And the thing works like a champ! I'm very happy with this setup.
Best of all, I didn't have to figure out how to remove the motion detector, audio alarm, and door lock wiring from the anti-theft system and try to put the truck wiring back to stock form!