If you suspect a harness, go to the thermostst housing and you will see a blue sensor..peel those wires back with your thumb and see if they crack or have brittle insulation.
I would also search this forum for a homemade code tool and go into the owner access code retrieve box with it [ in front of battery] .. That will tell you many things that you don't want to find out later.
I would also look at the right/rear of the head parting line from the block..that is where you will see oil seepage if the gasket is bad.
Pampered vehicles are nice finds, but these faults have nothing to with being prevented by pampering...they are a fault/weakness of that chassis. and one is more likely to have a problem with a low milage one b/c those faults have probaly not been addressed yet.
Here are all the code and that info for that chassis.
http://www.peachparts.com/shopforum/showthread.php?t=107630