Recently bought an '87 300D, and suspect a faulty glow plug--or maybe two. Between one and six key turns are required to light up the glow plug lamp. All plugs test good with an ohmmeter, and all pins at the relay have 12 volts. Is the next step a current measurement for each plug? Existing plugs have about 90,000 miles and 9 years on them. The holes were reamed when last replaced. The relay was replaced about a year before that, and there appear to have been problems with the GP light from then. I could also just replace them all and see what happens--maybe it's time?

Rob