battery drain after new head unit

Greetings all: I have installed a Pioneer DEH-P77DH in a '02 Suburban with OnStar. Since the install, there is an apparent drain on the battery w/o the ignition turned on (aux or run). Alternator output is normal (up to 30+ amps depending on battery voltage). Is there a way to check battery discharge when all is shut down? There was a relay included in the wiring harness but I don't see where the drain can be with everything off. -keevel"If you want an education, go to the library. If you want to get laid, go to college." -Frank Zappa

Thanks for the reply. The owner wanted to retain on-star capability but he is not currently a subscriber. I used the PAC OS-1 interface. I sort of figure this has something to do with on-star in that every time the battery drains to nothing (< 9 volts), once a charged battery is applied, the 9 pin harness to the OS-1 has to be unplugged and reconnected before there is sound to the speakers."If you want an education, go to the library. If you want to get laid, go to college." -Frank Zappa