Two ECT Sensors LS1 Where is the other one?

[eagleuh1]

Was this harness modified already. Perhaps they added wiring for a guage sender that some people put in the passenger side head at the back side. There is an allen head plug normally there. It will be below the heater blower/AC box. This is how I set up my 5.3 to supply the temp guage. The driver side sensor supplies the PCM with ECT signal.I can't recall what sender I used on passenger side, but believe it was 99 Fbody. Good luck. What color is the extra wire that you have? Pic of connector would be good.