I wanted to power it from the bulkheads. I duplicated a floating ground system like in this picture. I was hoping to not have to run additional wiring back to the trunk where the battery is.

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It is best to have dedicated wiring of the appropriate size, that way you never get a voltage drop at the ecu if something else on that line is drawing alot and causing a big drop.

Also, many people claim (I have yet to see hard proof, but it seems credible) that the capacitance of the battery will damp out transients and noise coming from other devices on the line (electric fans, waterpumps, etc...

It is a hassle to pull extra wires back to the battery (both power and ground) but I always set my systems up as such and have never had noise issues resulting from where I sourced my power and ground.

 

It true that the battery filters out noise just like big elect cap. We have encountered problems with all ecus by not grounding and powering from the battery. You can get all kinds of unexplained problems by not doing it this way. I just had a customer who put his battery + wire on the car side of the shut off switch, everything worked great but every once in awhile it wouldn't save changes instead it would revert back to the old tune. Direct battery for sure.

 

Thanks guys, that's sort of what I figured.

 

A friend of mine had the same exact problem with his BS3.

Wire to the battery.