91 camaro with 5spd 383 striker (was 305). When you turn key to start the starter isn't engaging all the way and grinds. Have replaced starter , starter relay , neutral switch both positive and negative battery terminals and checked all grounds on engine. Only thing that works is running a jumper wire with a push button. Would like to eliminate the need for push button starter. It's seems like there is not enough power going from key switch to starter solenoid

 

Hmm well if the jumper wire is working, then I would suspect there is an issues somewhere along the ling with the wiring to the starter (like you suspect not enough power getting to it.)

I would check the wiring to and from the starter first and see if there is anything amiss.

I know you said you checked all the grounds, but when I pulled my engine I was surprised at how many grounding points there were. One on both back sides of the heads connected to the bell-housing, the two spots near the battery, and the other I think near the smog pump (I'm going to have to remember this when I put my engine back in..) I would also make sure to check the ground wiring to and from the starter again and make sure they are cleaned up well.

I'm guessing that a power wire is either getting corroded near one of the contact points or has a break in the insulation and is getting corroded there. I know that several of my wires had that going on that I could finally get to and fix with my engine out.