Starter does not always engage when the key is turned. When it does start it sounds normal.

I have had the starter check and pass when I try to start the car it turns over but when I turn the key back to run the starter stays in gaged I checked the starter relay is good

I have a 1987 Z-28 TPI 350 i put in a 39 Chevy. I have rebuild the engine and it runs great. I have installed a new starter and solenoid ( also i have installed a new 21 fuse wire harness ) but the solenoid spins and won't engage the starter unless you repeatedly try starting it and it eventually cranks the engine and starts. Ive traced back the wires and don't seem to find any issues. I did a voltage test at the solenoid and a got 9v reading. Any trouble shooting tips would be greatly appreciated.

I purchased the car as is would not crank seller advised me it probably needed the key fob programmed. Did that several times I went through every ground I can find I can crank the car over from the starter relay so not a starter or locked up.

Electricity fully operational, no sounds at all from turning the key. If I let the car sit for 2 hours, it'll fire right back up. New starter, battery, and alternator already replaced. What should I do? I think the problem in in the fuse box but idk where to start.