I bought this off the bay from Trainz, which of course would have gotten it from someone else. It's an older MTH GP9. The box label says "Baltimore & Ohio No. 6603, 3-Rail w/ProtoSound." When I tested it on the track, the only thing that worked were the cab lights. After opening it up, this is what was inside. There are a number of disconnected molex connectors and other wires. Looks like the original owner attempted to install marker lights in the process, among other changes. There was no mention in the ad about any ERR modification - I'm sure they had no idea.
I assume this is a Cruise Commander. I've never installed one. I'm considering sending it off to someone to do a rehab.