2000S4B5

I had a rough timing belt fail with broken valves so I replaced it with a used motor from an A6. Just about everything is wired up along with two grounds, but I couldn't find a plug-in on the engine wiring harness from a loose wire on the starter/alternator harness. I took off the old plug in from my old engine harness and spliced it into the new one exactly where the wires led on both harnesses and wire colors. When I connect the ground cable to the battery it sparks. But when I connect the positive I get nothing and the car stays dead. Is the car in service mode and has to be reset? Or is there some connection I'm forgetting? Maybe the wires I spliced although are in the exact same location and carry the same wiring colors are incorrect? Both engines had APB written so I'd assume the harnesses are exact. I'd appreciate any help! Thanks!!