530 starter not cranking

[JimWA]

We have a 530 converted to negative ground before we bought it. It turns over when I engage the starter BUT if I quit cranking it over before it starts I cant engage the starter until it has sat for 5 - 10 minutes. Then the starter engages as normal.
How do I find the problem?

 

[Tx Jim]

IIRC the 530 starter solenoid is very difficult to access for checking voltage but one needs to check solenoid engagement voltage