KW starter issue

I have posted before about voltage drop tests. It is not rocket science. We need a meter as we cannot see electrons flow.
Probably something simple like a ground between the engine and frame or batteries. A simple test light will do the job. Two people make it easier.

 

Starter relay? Different motor but mine presents the same when one's going bad...

 

Does it still have the push on connectors for starter relay in battery box?

 

I had a similar issue. Truck would do exactly what you are talking about in my 379. Put a new starter in, same issue. Checked the voltage to the starter solenoid, at times was only 6-8 volts. Turned out it was the wire from my starter button to the solenoid.

 

I feel your pain. Hopefully it's an easy fix. I just ran a new wire to the started from the button. Good luck

 

Well if I am working on a break down ,like I am driving it with limited tools, I might cross the battery top terminal from the solenoid to the small one on the drivers side. It should engage and spin the engine.
That is a 42MT with the solenoid on top which you most likely have.
If you use the screwdriver between the two large studs the starter motor should spin without engaging the engine.
That is the kind of stuff that can ruin screwdrivers and damage threads. I do not like to recommend things that could have bad results. An example for the reason of voltage drop testing. Went on a service call for a similar problem. The starter had already been replaced. A test light between the positive battery terminal and the solenoid would light when the start button was depressed. The battery cable connector at the battery was in a sealed connector. It looked great but testing narrowed it down and I cut it open. It was all green and corroded inside.
Love to see you have her going pics!

 

That is to the large + battery stud on the solenoid. Do the same thing from a - battery stud the the big ground stud on the front of the starter.
All you need is a test light ( old school with a light bulb ) and enough wire to bridge the span. Have someone try to start it in each case. The light should not light.
Hold the test light on the small solenoid terminal nearest the frame. Have someone push and hold the starter button. The light should stay lit.
Happy 4th. What did you find?