with a 1984 300TDT w/ 184000 miles

My GP light doesn't always light up when I turn the ignition, and if I try to start the engine, even if I wait like 30 sec. it has a very hard time to start (eventhough temperatures are nice right now still). So basically if my GP light doesn't turn on it sounds to me that the GP are indeed not powered up. Sometimes it would just take a few times turning the ignition on back and forth for the GP light to come on -and then the car would start fine. This morning in spite of many tries, the GP light would not come on, and I did not try to go for a hard start (I could afford to take an other ride, not like I was stuck at work or something which would have required a hard start w/o the GP). I need to mention that I have changed all but 1 GP about 6 months ago (couldn't get to the 5th cylinder and decided to postpone this until I was going to do a valve adjust.); still the old GPs tested fine and must have been pretty new (no history from PO ).
Any lead appreaciated Thanks to all (great forum BTW