1990 Questions for all other cars car wont start when hot

I do not know what a holden jackaroo is but I'll give it a shot.
When you shut off an engine it actually gets hotter because there is no coolant flowing, or, if the engine is air cooled, there is no air flow. If your engine has a distributer cap try changing it. It may be cracked. If your engine has coil packs test each coil pack for the proper resistance at the highest temperature recomended.
A small distributer cap crack can expand enough to cause a spark failure. A bad ignition coil will do the same. Check the ignition module also.
The heat is causing something to expand too much.