To clarify the excellent answers already provided- As a *pilot* only, you can not fly an aircraft with known deficiencies, unless the specific issue is permitted by MEL. The MEL will provide conditions of permitted operation, i.e. with "door" caution panel light, you have to check every door prior to takeoff.
If you don't have one, it is a very good idea to get an MEL. It'll save you a lot of headaches.
Hint- count caution panel lights when you bring the battery up. Caution panel segments fail in both directions, dark and light. You wouldn't want to fly an unairworthy aircraft, especially as in your scenario:
"Main Gear Box Pressure or Temp light? My question relates to a situation where you landed out in the field, only to find on the restart that one of these was inop. Could you fly back to base so that it can be addressed? ps. there are no MGP or MGBT gauges."