hot engine won't start

[60apache4]

I have a couple questions about my 71 1-ton with a BB-402.

The engine won't start when it is hot so I replaced the engine wiring harness, starter, battery and ignition switch and it still does the same thing.

On the engine harness, what is the yellow wire for? When I hook it up as shown in the service manual and assembly manual the engine will crank and turn over but then shuts down. I disconnected it and it works fine, so I am thinking it is not used...Also, what is the heavy gauge pink wire for; I can't find it in the manual and my original harness didn't have one.

Also, I think I need a heat shield for the starter, so what are you guys with Big blocks running to shield the starter solenoid from the exhaust manifolds?

Thanks for your help.