91 240sx starter problem, automatic trans

[Thothren]

My starter doesn't seem to get any spark to it on my 91. My car was stolen, when they found it I started it and on the way home it seemed like the head gasket went out. It then turnred over real slow, but finally started. It finally stalled out about a block from home, turned over slowly once or twice, then wouldn't turn over any more. To add insult to injury, by the time I got a tow truck to get it home, some SOB had cut out my catylatic converter. I got a replacement engine and swapped it out, but when I turn the key I get nothing from the starter. Had the starter tested at the parts store, they said it was a bit weak, but it would still engage. When I try starting it I don't even hear the solenoid click, but I do hear a click from a relay or something someplace. Can anyone give me some good troubleshooting steps. I am an FAA certified Airframe and Powerplant mechanic, but electrical systems are a weak area for me. I've been reading the forums, if I have a bad ground, will I not get 12v at the starter when turning the key? Can someone tell me the location for the grounds so I can verify that they are connected and tight? Thanks in advance!