The car has been running great. One day when I turned the key to start the car, I heard a buzzing whistling noise from under the hood. Upon investigation the noise came from a black box on the driver side close to the front of the car. There are two connection boxes hooked to it. I would greatly appreciate any help I can get to get this car running again. Thanks.

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1980 - 300D
1984 - Mazda B2200 Diesel

It's the glow plug relay making a sound like that chances are it shorted out possibly got moisture inside.

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1984 300D Turbo 200K

One night I had the battery on charger and left the hood open. It rained heavily that night . You are correct. Moisture must have gotten inside because after the rain it would not start. What is the fix? Are there ways to bypass the relay and start the car? Thanks a lot for answering my question and helping me.

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1980 - 300D
1984 - Mazda B2200 Diesel

Physically possible, yes. Recommend, not really.
Emergency start: jumper power to each glow plug for a few seconds (as long as your glow plug light usually stays on) and then immediately crank. Not something I really recommend especially if you aren't comfortable with electricity and sparks. There is a plug at the front of my relay (6 gang, only 5 used) for the wires to the glow plugs. TRACE THEM BACK TO VERIFY THEY ARE THE CORRECT ONES. Wherever you make the connection the arc will eat away at the metal you use, so a sacrificial piece of metal is a good idea in the plug.

I WOULD STRONGLY RECOMMEND JUST REPLACING OR FIXING THE UNIT SO IT WORKS PROPERLY. And not trying this.

Thanks. By fixing you mean take the box out, drain it and dry it and put it back? Or do I have to buy a new relay box? Thanks.

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1980 - 300D
1984 - Mazda B2200 Diesel

You can buy a used relay box.

Sixto
83 300SD

Depending on how nice the car is and your desire to spend money on it, I have read about people rigging up a manual glow plug controller as well. (Button in car) A search of the forum should show that set-up. Less risky than the method I mentioned earlier (the main reason I don't recommend it is the risk of shorting to a part of the fuel system.

This is worth a try. Then a used relay is a good option if you can find one.

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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.

Why does the starter care if glow plugs are on or off? Is there an interlock?
Some years back I remember someone had a schematic using a Ford solenoid to replace the whole glow plug circuitry. There was no interlock and it was independent of the whole car circuitry. What am I missing? Thanks.

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1980 - 300D
1984 - Mazda B2200 Diesel

Who said the starter cares that there's a glow relay? Through most of the '80s the starter signals the glow relay to stop glowing. Later it signals the glow relay to start the afterglow timer. The glow relay goes through a full time cycle without that signal.

Sixto
83 300SD

So how come the starter is not turning?

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1980 - 300D
1984 - Mazda B2200 Diesel

Weak battery? Short inside the glow relay not allowing enough current to the starter? Worn shift rod bushings? Bad NSS? Could be a lot of things but start by removing the strip fuse in the glow relay. If the starter still doesn't turn, it's not because of the glow relay... which could still have its own problems.

Sixto
83 300SD

Sorry didn't realize starter was not turning. I have interlock issues occasionaly with my '83. I am able to make it crank by bridging the terminals for the starter solenoid. On the top of my right wheel well under the hood there is a 2"x1" box with a flip top cover. It has 3 terminals with philips head screws. I am able to bridge the front and rear terminals with a piece of solid 12ga wire and it cranks. I have also been able to use a folding pocket knife in a pinch. Make absolutely certain that the car is in park with the emergency brake on. You should be able to see that the wires run down to the starter. Sparks aren't too bad, just need a thick enough wire so it doesn't heat up.

How do I identify the strip fuse in the glow relay and how do I get to it. The car ran great. I know rain got into the relay box. Thanks.

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1980 - 300D
1984 - Mazda B2200 Diesel

Fuse strip is a flat piece of metal bridging two screws near the rear (iirc) of the box. I've heard people say that they can be cracked but not look like it, although never experienced a burnt out one myself.