Ignition issue

[93 Z32]

What happens if your ignition/starter relay is going out?

Here's my issue. Did a plenum pull to replace injector. Ran amazing after job was done. Next day, got up and tried to start the car. Everything in the car worked, lights, dash, radio, turn signals, fuel pump primed, car just wouldn't turn over. Wouldn't turn over all day. Went out later at night, car fired right up. Went out this morning, car fired right up.
Talked to the previous owner, he already replaced the PTU. I ordered a PTU sub harness from Z1 this morning. As the harness is badly corroded.
Do u think replacing the sub harness will fix this issue? Or could it possibly be related to the ignition relay going out?

All coil packs are good. Just replaced plugs with new NGK plugs. I get all my parts from Z1.
Oh and all my ground wires are intact and tight. Everything back in its original place. I'm no slouch with a wrench. Just never had anything like this happen.