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Old 08-31-2018, 12:50 PM   #1
Wayne Suhrbier
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Default Help Identify component in trunk light wiring

Does anyone know what this is and or for? It doesn't look OE. It was placed in line with the wires for the trunk light in a 06 STI. Trunk light works fine without it. Everything else in the car works fine also without it.



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Old 08-31-2018, 02:33 PM   #2
Mulder
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That's a diode. It's there to allow current flow in only one direction, presumably to avoid some unwanted interaction. Probably alarm related.
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Old 08-31-2018, 02:48 PM   #3
mrsaturn7085
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This is OEM, and it is to provide a voltage signal without allowing a current sink. There are a few of them located in the OEM harness.

Check out my AUTO I/C thread sticky in the Management forum if you want to see one of the OEM uses for these:



In this case above, pin L of the ECU is receiving a "AUTO spray active" low-side signal through the AUTO switch component when depressed. If pin L was a low-side pin, it would illuminate the light in the AUTO switch without the diode there any time the switch was depressed (even if the water tank was low). It would also sink current through the ECU pin which may exceed maximum allowable current through the internal ECU circuit.

Last edited by mrsaturn7085; 08-31-2018 at 02:56 PM.
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Old 09-02-2018, 02:42 PM   #4
Wayne Suhrbier
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cool, thanks. I'll go ahead and put it back in.
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Old 09-05-2018, 09:45 PM   #5
jasonwrx86
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As an electronics engineer this is what's called an ESD protection diode. Usually to dissipate high voltage electrostatic discharge when touching the wires when air is dry so it does not fry the circuit.
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Old 09-06-2018, 11:40 AM   #6
Wayne Suhrbier
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"air is dry" that's a good one Alabama never has dry air. But seriously its good to know. I couldn't think of a reason to have a diode in the trunk light circuit.
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Old 09-06-2018, 01:44 PM   #7
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Quote:
Originally Posted by jasonwrx86 View Post
As an electronics engineer this is what's called an ESD protection diode. Usually to dissipate high voltage electrostatic discharge when touching the wires when air is dry so it does not fry the circuit.
Look at the diagram I posted - this is not for ESD protection... this prevents the ECU pin from sinking current and turning the indicator lamp on. This forms an integral part of making this circuit work and is not for ESD.
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Old 09-06-2018, 02:04 PM   #8
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Quote:
Originally Posted by jasonwrx86 View Post
As an electronics engineer this is what's called an ESD protection diode. Usually to dissipate high voltage electrostatic discharge when touching the wires when air is dry so it does not fry the circuit.
ESD/EMI, doubt it is either one. Taken from a field service guy/facilities guy for close to 40 years.
My normal issue is between engineers vs. field service.
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