Ground wiring: NA 1.6 90-93 JC-02 JC-03
 

I am trying to track down higher rpm/load noise and suspect it may be coming from my use of OE grounds. Shop manual diagram shows JC-02 and JC-03 connected - which puts a bunch of power grounds in the same ground circuit as my sensors. That said, when I was going through the wiring, I found a jumper between the ring terminals for JC-02 and JC-03 at the back of the cylinder head. It did not look factory and wanting to separate the power and sensor grounds, I removed it. What I want to know is IF that was the connection highlighted in the diagram OR is the diagram connection somewhere else? and if so, where?

http://fe3miata.com/pics/miata-gnd-connection.png

There's a spade connector on the back of the intake manifold that ties both signal ground and power ground together on the na6 loom. If you cut the black wire with a green stripe you'll separate them and should clean up a lot of noise.

Thanks- You think that's what the ominous red circle area is indicating? I did that and have the black power ground circuit and black/lightgreen sensor ground circuit separately anchored on adjacent bosses at the back of the head. I am not using the AFM or NBO2 leads- of which both have the shields tied into the black/lightgreen sensor ground circuit right next to the ECU connector, so I'll clip that and remove it from sensor ground circuit. I did not find any connections between the two ground circuits near the ecu connector.

Don't ground the black/lightgreen wire to the head or that will create a ground loop. Just leave it floating.

Thanks - got it, sensors ground at ecu, ecu grounds at head.