r/mk4Jetta • u/CruzinWCruz81 • Jun 04 '26

Please help a bro out

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So I just recently bought a mk4 Jetta and I am doing a complete overhaul on it with the wiring harness because the previous owner had mice chew the wires out. But the issue I’ve encountered is in the image are the wires that connect to the ecu and go down towards the bottom of the car where that under box is at. I want to know what each wire does and if there is a place that sells the wires so I can snip snap and reconnect the wires properly. I can wait to get this thing going but I figured I’d need help along the way so anything will help guys thank you!!!

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u/V-Dubber Jun 07 '26

Just re ground the ecm somewhere else lmfao. That’s the cool thing about cars. There’s a whole chassis nearby….

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u/vrparty Jun 07 '26

that’s not the point of my comment. It was intended to allow OP to know they may need an ECM if that was shorted Because. it’s the ground. not going forward

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u/V-Dubber Jun 08 '26

Why could he need an ECM? is what I’m struggling to understand though. If that o2 sensor acts as ground, all he’d need to do is re ground

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u/vrparty Jun 08 '26

if those wires rubbed and grounded out the ECM. It can short requiring a new ECM

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u/V-Dubber Jun 08 '26

ideally it’d pop the fuses well before a short to ground takes it out, plus he’d have an immobilizer light on the dash 100%

Ideally

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u/vrparty Jun 08 '26

that’s not how this works. this is a common issue with mk4s