msd 7 digital

Anybody running this box? Have had one for a long time. Would run fine than refuse to start. Swap a 6 in and no more problems. Did the troubleshoot thing. ( no spark) and even sent it back to the factory. They said it was fine. So I'am going to try it again. Put together a very basic harness for the car as the stock harness was a rats nest. Going to focus on the grounds. Any thoughts or tips? Thanks.