I have a 79 300cd, I noticed shortly after purchasing it that it has a transmission vaccum valve [that is not hooked up] mounted on the injector pump, I could not locate a modulator on the transmission,I later read that79 models did not use vacuum for transmission control....hmmm I thought that maybe someone had changed the pump with one from a later model. then one morning it got cold and it wouldnt start, time to check the glow plugs, i had read that 79 and older used loop style,but it turns out that mine has pencil style with a home made wiring harness.I purchased an autolite glow plug for a 1980 300d,[just took a guess] from a local parts store and it doesnt fit! looks the same but the shoulder is a hair bigger then the original bosh plug. Now I'm stuck! Here is the numbers off the engine,617 912 12 105 499. the engine does not have a turbo or an egr valve. can anyone tell me what i have from this information or point me in the rite direction to find out?