Burning HOT Preresistors - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 07-12-2005, 09:28 AM Thread Starter
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Burning HOT Preresistors

I just burned the Bosch symbol into my finger tip!

After leaving the ignition on for about 5 minutes and having not run the car at all, I felt heat coming off the two preresistors and smelled that unfriendly hot electrical smell. Smartly, I pressed my finger on the bracket that holds it and realized too late that it was not a good idea. No wires show any melted or chared insulation. The coil is warm and no other wiring seems to be unduly hot. The Ignition Control Module in the left wheel well seems only slightly warm. And the car seems to run fine, except for some odd beahviour (tach jumps, rough idle sometimes) that I have been chasing for a while now. My other posts have looked into those...

My friend who is fairly knowledgable with mercs (I thought I was...) said that this in not an abnormal condition, but I cannot believe it. No electrical components should ever normally run that hot unless there is some other condition ocurring or the resistors are about to go.

Why would they be hot enough to leave a burn on your finger (no blister yet)?

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post #2 of 2 (permalink) Old 07-14-2005, 02:00 AM
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RE: Burning HOT Preresistors

The pre resistors for your ignition coil normally gets hot even whe the ignition is just turned on. current flows from the resistor thru the coil so this will make the resisitor warm.
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