I'm not familiar with the Snap-on scanner, does it use OBDII or the connector under the hood? Does it read SRS codes? I ask because with the Peake tool, there is an entirely separate tool for SRS. If anyone near you has a Peake SRS code reader, borrow it.
No codes with light off or on? That sounds like maybe a bad connection somewhere. Possibly shorting, possibly bad ground. Tough to say without codes.