How does a garage door opener button work?

[DaOld Man]

Ok, Ive got an Overhead (brand) garage door opener.
I have made a combination lock circuit which I would like to use to open the door from the outside of the garage.
The circuit I built will basically "short out" the two wires going from the door opener unit to the (inside) wall mounted button, if the proper combination is entered from a 12 digit keypad.
I would like to use an opto isolator to short out these two wires.
But it wont work.
The inside wall button has a button to lower/raise the door, a button to turn on a lamp that is mounted on the opener unit, and a switch that can disable the button and the radio remote (for going on vacation or whatever).
The wall button only has two wires going to it.
I can short out the two wires and the door will raise or lower.
But if I use an opto isolator to short out the two wires, it wont raise the door, but it does turn on and off the lamp.
My first guess was that it is probably an AC signal.  AC coming back to the unit will raise the door, but a DC will turn on the lamp. I theorized the lamp button probably placed a diode across the two wires, same effect the opto isolator would have. But I tried a solid state relay, which can switch AC, and it still just turns on the lamp.
So what is going on? Im afraid I will break the wall button if I try to take it apart to see whats inside.
And how is does the "vacation" switch work? With this switch turned to "lock", shorting out the two wires does nothing.
I have searched the internet trying to find out what is going on with this probably very simple circuit, but I cant find anything.
I guess I can use a relay for my project, but I really wanted to stay away from relays, due to physical size and power requirements.
Can anyone give me some insight on this?
And BTW, if anyone is interested in my combination lock circuit, I will be glad to post schematics and pics, although it is way off topic for this forum.

[HaRuMaN]

Don't know the answer to your question... but, my vacation switch:  I unplug the motor.   

[HaRuMaN]

And as for your Keypad... why don't you just buy one of these?

http://www.liftmaster.com/consumerweb/pages/accessoriesmodeldetail.aspx?modelId=1274

[DaOld Man]

Just about got it built, besides, I like Build Your Own.

[kamushekar]

Hi,

Can you post the schematics on how you were able to build it out?

[DaOld Man]

Im just now seeing this, and I got to get to work right now, but yes, I can post the schematic later.
Hopefully tonight.

[kahlid74]

Have you monitored for voltage?  Maybe a difference in voltage causes a difference in function?

[DaOld Man]

Kahlid74: Its been around 2.5 years since I was investigating the button problem. I cant remember if I tested the voltage or not. I wound up using relays and the circuit works pretty good. No problems at all.
I posted the circuit in Automated Projects:Circuits, because I thought that might be a better forum for it.
I wrote out a very lengthy description, and when I posted the pic, I got an error because of the pic being a bmp, and I lost everything I typed. (Dang it!)
So I just re-posted the pic as a JPEG.
Kamushekar: if you really need a description I will type it again. Heres a link to the circuits thread, scroll to the bottom to see the schematic:
http://forum.arcadecontrols.com/index.php/topic,129533.msg1356246.html#msg1356246

[lilshawn]