need help...car show tomorrow...electrical issue?

I recently changed out my starter relay on my 72 Dart (318 powered). I was having an issue with the car just suddenly not starting. When you would turn the ignition key over, everything would be normal however the engine would not engage. I thought it was that relay but now it is doing it again. Basically, the motor will just randomly not engage every now and then. I can start the car by jumping the starter relay.

Of course I am an hour from home at my parents cabin for a car show tomorrow. Any ideas as the solution for this? Thanks.