Vazquezanator

So, I own a 260z, and when i bought it, the previous owner had a 240z dash installed. Car ran. i then bought the correct dash, and the correct wiring for it. but, now the car only turns over if i hold the key in a certain position. if i realese it, its shuts off. i didnt change the ognition switch. till later, and the new one did the same thing. idk what it could be. anyone encounter this problem before.