I bought two systems on ebay for less than $30/each shipped (one for the 740, one for the 780.) They are apparently from some Asian country with a manual written by someone for whom English is obviously a second (or third or fourth) language.

I could make out the wiring diagram okay, but the instructions require reading between the lines. Example: "In arm, the system will be triggered while the door is opened, the vehicle is hit or towed up, the siren would chirp loudly, the flash lights would gleam, the engine would be cut off. The siren will stop chirping automatically after 60 seconds while the system would again." And another: "After the ignition off 10 seconds, the siren will chirp 3 times, the flash lights would gleam 3 times also to remind arming the system."

Since my wife's 740 had no actuator in the driver's door, I had to install one (also procured on ebay) and since that lock controls all the others, I just wired my keyless entry to operate the new actuator. I hooked up the siren and lights, but didn't bother with the ignition cut-off or the power windows-up function.

My 780 has actuators in both doors, so it should be easier to install that one (haven't done it yet.) I don't care that much about the alarm part, but it's hard to find a two-remote system without the alarm, and I did have a car stolen from my workplace in broad daylight in 2001. It was an '85 Camaro and I got it back the next day smelling like body odor and sans radio, subwoofer, tools etc. I do have a starter kill on that car now. But not too many car thieves want multi-hundred thousand mile Volvos.

I also installed a locking system on my '81 240 wagon a couple of years back. I love the convenience, and when out on a date with the little woman you can chivalrously put her in the car without having to unlock two doors by key.
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Kenny H Three SUVs, four cars and seven motorcycles