Connect the power door lock to car alarm?

I bought an alarm system for my car. I installed it and everything work nice and well. The system is a Audiovox TSP 575 which costed me $30 to get.

The system has an option to hook up to a door lock interface that connect the siren control module to the power door lock system of the car which add on a keyless entry feature so it can lock and unlock the door when the system is being armed and disarmed.

The problem is that NOBODY sells that door lock interface unit. (AA 9158) Or it is VERY expensive.

I feel that I can make a door interface unit myself, I just need to know what parts I need.

There are two wires come out of the siren control module (1 pos and 1 neg, 12v) and they switch from positve to negative and neg to pos depend if the system is armed or disarmed.

Now, I have the power door lock in the car. I took it apart and it has 3 wires. 2 Pos and 1 Neg, 12v. 1 pos (let's call it A) control the locking process and the other Pos (B) control the unlocking process.

What I need is, that a circuit system that controlled by the 2 wires from the siren and can temperory connects A to the Neg when the system is being armed and B connect to Neg when the system is disarmed. I just need them to connect for half a second or so because I don't want to burn out my door lock motors.

So, how do I go about making this unit. What parts do I need, where can I get it, and how much $$$ am I looking at?

Thanks for your time.

I have a 93 Saturn SL2 if that matters.

Doesn't work.

The alarm doesn't give out "PLUSE" voltage.  It gives out "CONSTANT" voltage.  One positive and one negative.

I need something that give me a PLUSE whenever the voltage on the two wires changes.  That would SLOVE all my headaches.