Ground wire

Hi, I have a 1991 ford tempo with a ATX transmission, which we just got done replacing after a week. We had to practicaly remove the engine. Now it wont start and never had problems with starting before, fan come on so it getting juice. We think it the battery ground, but silly us dont remember where it grounds to, we ground it to the firewall and the engine block but nothing, were thinking it grounds to the tranny somewhere, but not sure where. And had starter tested to rule that its fine. So if anyone knows where the ground goes or if you know of something else that would cause it not to start. A response would be greatly appreciated. Thank you