Last weekend I put in an alarm on my 99 f150. I discovered when hooking into the power locks that the alarm was not polarity sensing or a dual polarity so I wired up 2 relays to make the negative pulse work. It works great for the passenger door but most times when it pulses the drivers door lock actuator just groans and doesn't move. I've wired the relays with no splices in any wire, used 14 ga wire and lubed the latch heavily d/t the notorious dome light issue. Nothing really gets the door to reliably lock. I even switched my relays from lock to unlock sides to rule out the relays as the source of the problem. The door locks with all factory controls. Just not from the alarm. I hooked up under the high drivers dash to the lock/unlock wires. Have I missed something or is my actuator just tired?

 

It may be tired. What you can do is put a meter on it, and watch it while you actuate it with the alarm system, and then the factory switches. You may have a little bit of voltage drop in your wiring, making the difference.

 

I usually put the relays in the door just under the switches plate and run twin-lead speaker wire back out of the door to the alarm or keyless entry.
The factory locks are 5 wire reverse polarity.

Unless it has OE keyless entry then its negative trigger, no relays needed.

 

I rewired my relays this morning with 12 ga instead of 16 ga power wires and that was all it needed