Does anyone know if that 3rd brown wire goes to the knock sensor? 93 rx7. I can't seem to find another wire that would go there. Thanks

 

What you want is find the connector plug that fits the knock sensor plug. Look at the pic.
good luck..

 

^^^Suppose the problem there is, commonplace for the knock connector and wire insulation to cook and break - spade connectors often replace them.

Doubt the brown wire is the one, it's white on a rhd near than vintage. Unless it's an optical illusion.....or there's been a cut and splice, the gauge looks entirely wrong too - it's closer to the sizes in that wire bundle on the lhs. The wire is shielded in the harness if you unravel some of the electrical tape. If there's doubt, probing 3M in the 16 pin ECU plug and the wire itself should reveal all.

 

the brown stuff is the protector for the shielding, the actual wire is under that, you're looking for a white wire (i think, the O2 is the other shielded wire, and its black, or the other way around)