1998 V70XC Aftermarket Keyless Entry install

[everwiser]

I did a basic search and there were over 400 topics for "keyless entry", so what's one more? On page 74 of this link: http://www.scribd.com/doc/28783687/volvo-c70-s70-v70 shows the Volvo remote control receiver (device 4/19). According to another page in the Scribd link above, this unit is mounted high up on the driver side of the dashboard. Provided I can get my hands on the stock receiver, I should just be able to swap it out with my aftermarket unit ($14 on Ebay). According to the schematic there's +12V and Common plus three signal wires. Judging by the NPN transistor symbol on 4/19, it should be a matter of pulling each of the 3 signals to ground to activate them. My question is "has anyone done it this way before"? If so, which wire corresponds to which function? I'm sure two of them are "lock" and "unlock". Is the third one "trunk release" or something else? When I bought this car the PO couldn't find any of the fobs to go with it so I don't know what the third button would have been but my gut says "trunk". Any guidance is greatly appreciated. Thanks!