1999 Chevy Tahoe ECT Sensor Circuit High Voltage

Welcome to the forum. Thanks for the donation. My info says it is located, right front of engine, on or close to thermostat housing. The wiring colors are yellow and black. The yellow wire carries 5 volt reference. If you use a digital voltmeter, as the coolant warms up, that reading should slowly drop.

The black wire is a shared circuit for ground. It's not unheard of for another sensor to cause ground problems.