2000 Blazer keyless Entry

Hello, Can anyone help? I just bought a 2000 blazer, it has PWR locks,Windows Etc. Remote keyless entry was an option but was not factory installed. I purchased a factory keyless entry receiver with two remotes-Receiver Part # 15042969. I was told the connector for the receiver is under the lower left dash panel. I found one that fits and plugged the receiver in but I cant get it to work. even though the remotes are factory programmed to the receiver I tried to get it into programming mode by holding the unlock button and cycling the key from off,on,off,on,offand releasing the switch. I got no conformation that the receiver was working. Is there something else I need to do to get this working? Thanks

Rob