Preglow Indicator 83 300D

Hello Everyone,
A few days ago my preglow indicator stopped illuminating. The glow plugs function fine, as I can hear the relay and the engine starts normal. I
checked the bulb on an external 12V source and it was good. I also verified good connection in the socket. Does anyone know how to go about troubleshooting this?
Thanks, Jeff
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Check the fuses?
If fuse is really OK, not just looks OK, then the glow plug relay may be the cause - in which case I'd leave it alone. The light just tells you when to crank the engine and you already know THAT!
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Thanks for the reply.
I checked the fuse box for a fuse indicating it served the preglow indicator circuit and didn't find one. I also haven't noticed any other electrical items not working. Do you happen to know which fuse it may be?

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No idea as to which fuse to check. A wiring diagram will show it.
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The main bus fuse in the glow relay is the fuse. But it will be fine.
HOW did you check the glow plugs? With a ohm-meter? With a test test light? IF yes to either or both, then you did it wrong. The REAL test is with an ammeter and a remote starter switch. Disconnect the big connecter on the glow relay. Connect one lead of the ammeter to positive on the battery. Connect the other ammeter lead to one end of a remote starter button. Get a long skinny screwdriver and connect the other lead of the remote starter button to the shank of the screwdriver. Now touch the end of the screwdriver to the threaded end of the glow plug. Press the button and watch the ammeter. Initial draw will be 25 amps. As it heats up it will drop to 10-15 amps after 10ish seconds. If it reads ZERO when you press the button, it is dead. If it climbs, 30, 40, 50A, it is bad. And yes, the ohmmeter test will show it is good until you apply current! Be especially mindful when testing #1 cylinder glow plug, IT is the one that controls the dash indicator light. The glow relay has built-in fault indication: it will make the dash light blink after starting the engine if one or more glow plugs are bad EXCEPT for #1. #1 controls the light. If you are going to replace some but not all of the glow plugs beware, they come as 9.0V and 9.5V. You don't want to mismatch them. Look on the old ones for the voltage style you have.

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You may have an open glow plug. Check number one first. They should all measure less than one ohm. It's probably starting OK because the other 4 are OK but the cylinder with the open glow plug will cake caked up with carbon. Autozone has them for abour $13.00.
--

73
Hank WD5JFR
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Or the indicator bulb burnt out!
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CaptainW116 wrote:

I checked the bulb on an external 12V source and it was good.
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Thanks for all of the info. I think I will try replacing the #1 glow plug to see of that helps. I have noticed lately it hasn't ran quite as smooth as normal right after startup, although it runs OK.
I appreciate all of the replies!
Jeff

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