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Motec wiring

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hello guys,

I would like to have your feedback on the method of wiring all the shielded cables drain to the ''0V sensor ground'' pin. It seems the other ECU's I have dealt with have an appropriate pin for drains. Why would you want to have your 0V spliced up with all the noise coming from the drain shielded cables ?

It seems that method would offsets the ''true 0V'' of all the sensors connected to it.

Thanks !

Please provide more details -- is there a specific MoTeC harness or drawing you are referencing? I normally connect my shields to the chassis ground.

Internally I believe most MoTeC products connect the 0V to the Batt- with some kind of filter, so it's not really all that bad using the 0V.

I think he's refering to the fact that all of motec's factory (unterminated flyinglead at least, and probably terminated) harnesses collect the SYNC and REF drain wires to the 0V pin and then branch off. At least that's what I've seen on every harness I haven't built myself, so a dozen or so.

EDIT: I'd also point out that I believe all of these harnesses were sourced by customers from JGM automotive/Motec West, not sure if it means anything but I've also had at least 3 leads pop off the pins in my estimation too easily as well as have had more than a couple un-flowed solder rings on these same branches/collection points that I've taken on myself to repair. These are just observations and not a bash.

Thanks for the info. I have only built one harness many years ago from the unterminated harness kit. Since I have all the materials in stock, I just make mine from scratch.

Thanks for your input guys.

I know the older gold boxes use that method. I have attached a wiring diagram for an M800. I also found a drawing on the motec forum for an M130. It is the unterminated loom that you can buy from them. They still do that same method.

Let me know what you guys think. I always did my harnesses with the shielded drain separated from the sensor ground. I just want to know what is the best way to do it.

Attached Files

Thousands of cars have been wired using the M800 wiring diagram, so I don't expect you will have an issue. If it was a problem, I'm sure MoTeC would have changed their design / documentation.

Im sure there is no issue with that method. I was just wondering why they would use it. I see that you use a chassis ground for your shields, may I ask why you are not using the 0V instead ? Do you still connect your main ecu power ground to the same ring terminal or you separate the two ?

To me, this would tend to bulk up the 0V splice points with pretty much everything connected to it. I know the M1 uses two 0V but even with two 0Vs, I prefer to use one only for crank\cam and leaving the other one for all the sensors.

Thanks again David, your help is always appreciated.

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