cooling problems

To start off with I changed a leaking water pump on my 2.3L Q-4 engine. Worked fine and then later on I noticed a leak on my plastic coolant outlet pipe. Replaced that item, drove the car for a while and the plastic "wall" on the radiator starting leaking. Replaced that. Before I go off for a nice sunday drive I would like to know if I have a problem in the engine causing these leaks. I ran the car after the radiator replacement and the cooling fan did not come on. Check the cooling fan it was fine. I also checked the coolant tempature dash light circuit by grounding out the dash light wire the light did not come on, I would think that the light should have come on. Anyway while I had that prementioned wire disconnected from the coolant tempature unit the fan start up, engine was running. I then went to check the "codes" from my service engine soon light. I grounded out the terminals underneath the steering wheel and the "light" did not flash at all when the key was in the on position, just stayed on. Bought a new coolant temp. sending unit hooked it up,but did not thread it into the outlet pipe and started the engine. Slowley added heat, but the fan did not come on. Completely stumped by this perfect example of why GM MIGHT be in trouble.