W124 electrical behavior

I had a problem with my 87 300D and had to pull the battery for a day. (Don't ask me what happened. It's embarassing.) Anyway, before the battery was pulled, the glow plug light would come
on every other turn of the switch. Now, it works properly. It seems the circuit required a reset. Strange. But then, the w124 series did have some electrical anomalies.
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W124 Diesel glow plug system is not hard to fix. Here are a couple of things you need to do.
1. Make sure the battery is new enough and got full charge. Most places will test your battery for free. Autozone got the best bang per buck for group 49 battery.
2. Check your glow plugs by simply unplugging the plug from the glow plug relay and check the resistance from the plug to ground (chassis). It should all be like 0.5 or something like that. Make sure you got good battery in your multimeter to do this test.
3. If all your glow plug check out okay and the battery is new/good. then it is possible your glow plug relay is bad and you need a new one.
4 One last possibility is your ignition switch is wearing out so if you high mileage car is giving you a bit of problem starting or AC fan issue, then it is time to change it along with a new tumbler. You don't need the entire ignition lock... just the switch and tumbler (tumbler: get from dealer and they will match what you have and one brand new key.).
That's it!
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I have suspected the ignition switch all along. But the relay I had not yet considered. Thanks.
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When I said starting problem, I meant starter... not glow plug system.
Glow Plug Relay is much more sophisticated than we think.
1. It checks the continuity of the glow plugs... if two ore more glow plugs goes bad, it won't turn on glow plug light upon startup... then after we start the car, it will light up the glow plug lights for a couple of minutes and then disappear.
2. It will check the battery condition, the the battery voltage is too low, it too will not light up the glow plug light on startup but will show glow plug light later after startup.
I can't recall if it has another feature on it... but it is just not a simple relay.
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