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Best place to splice drain wire

Practical Motorsport Wiring - Professional Level

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When I say drain wire, Im referring to the wire in a solder sleeve connected to the shielding for a cam sensor, crank sensor, etc.

From what I've learned from opening up OEM harnesses, it seems a lot of manufactures choose to splice the drain wire in with the chassis grounds of the engine harness. This makes sense to me, as any noise caught by the shielding would just be sent through the chassis into to the battery, isolated from any sensitive circuits. Although, I have heard from multiple people now, whom I would consider knowledgeable, that they splice the drain wires to sensor ground when they are building a harness. It would seem to me that you would be allowing any noise that was absorbed by the shielding to enter the isolated sensor ground circuit and would defeat the purpose of even having it.

I am no electrical engineer, so my understanding of this could be very off. Hopefully some of you can educate me on the way its done at the highest level of motorsport wiring.



I prefer using the chassis ground. It's important that it only be connected at one end.

Gotcha, any explanation for your preference?

Also, ya I would never terminate both ends of the shielding, just curious about where to splice the one end of it, and the reasoning behind it.


I think chassis ground is just easier. You would already have several zero volt sensor wires trying to get onto the 0V ECU pin. OEM applications seam to use chassis ground that I've seen, so that's good enough for me.

There is a case where you can sort of have a drain at either end. That is when the shield does not continue through a bulkhead or engine-to-body plug (as seen on a Subaru diagram). But this is where you have 2 shields, the engine side shield is grounded to the engine, and another shield on the other side of a plug is grounded to body.

Do Zack and Andre not always chime in on forum posts?

Zac quit. They are trying to hire a new wiring guy. In the meantime you got me :)

Oh ok, well then I appreciate the response!

OEM manufacturing is aimed to produce as cheap as possible from one side and reliable from another. So quite often you will see that shielding is terminated to the engine block or chassis ground. Aftermarket ECU`s have specific dedicated shield output. This simplifies wiring a lot. Some ECU have over current protection at the shielded outputs. However more information could be obtained from a specific ECU manufacturer.

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