Trans wont shift to 3rd, how to test the igniton switch (IGN0)

The trans was not shifting quickly into 3rd as should for over a month. When it shifts the RPM would go up 1000rpm then shift and shift into 4th just fine after that. I drove the truck all day and parked for about 3hrs, went to run errands and the truck wouldn't shift into 3rd until I got up to 5k RPM and would have to keep RPM at 4k or above, if not then would go back in 2nd. Now I went to start truck to pull in back for solenoid change (2-3) the headlights did not come on as usual, was dark and come on by sensor. I moved the truck, turned off and the lights started coming on as usual with key. Then the check oil level warning came on in message center but after turning key on/off about 5x the check oil level message did not come back on. I tried again this morning and the oil light still doesn't come on.
1) Would the problems occurring be cause of a bad ignition switch, resistive or not appropriate voltage in IGN0?
2) How do I go about testing the ignition switch voltage
3) where is the ignition switch located to check connections?
Ignition switch I am referring to is not the key tumbler set but in fact the harness which operates all components.