The glow indicator light in the dash of my '77 300D is not lighting, however the car also does not start. I changed all 5 plugs, the 50amp in-line fuse and the ground wire. Indicator still does not work and the car will not start. My next step is to check the relay, however I do not have an electrical manual yet. I know it's in the dash somewhere, can anybody help me out?

Second thing is that the plugs are all getting power. I'm under the assumption that if the relay is bad, power wouldn't flow to the plugs. Please advise.

On the later cars the GP relay is in the engine compartment on the driver's side wheel well and probably the same or close with your car. If it's working you should be able to hear a "click" when you turn the key to the glow position. If you are getting full power to the glow plugs when you leave the drivers door open at night you should see the interior light dim when you glow. If no "click" or no noticable light diming then it's probably a relay or low voltage problem. Also, are you sure you are getting fuel? If you have an air bubble in the fuel line you can crank all you want and it won't necessarily start. Lastly, if you have the early loop type glow plug setup ALL the plugs need to work to get proper glow on even a few cylinders. Do a search here and you'll find lots more info on troubleshooting the loop type system.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

ditto the above post ... sounds like a bad glow plug.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Just because you replaced all the glow plugs doesn't mean that they are all okay now. They could be bad out of the box by being dropped or whatever. Take an ohm meter to each glow plug terminal at the relay and make sure they all read 0.6 ohms. If any are infinite, you've got a bad one.

Len

Thanks for the info guys. I have a couple more questions...

Is it possible to start the car without the plugs working.....it's about 85F today. Probably depends on how much compression the engine has.....if the valves are okay, how long should I crank before the engine would turn over?

I also noticed that the connector wire to one of the resistors blew off when the glow plug went bad. Could this be the problem? What function do the resistors play in engine starting?

What does this resistor look like? Mine have wavy wires running from one plug to the next. Check for voltage on the wire between first and second plug to ground. You should see about 2.5 - 3.0 volts. If you see any voltage you know the back four plugs are OK. If you see about 12 volts in this spot then number one is bad. You can continue to check each spot and the only place you should see 12 volts is on the tip of number 5 plug.

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1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C