So I got a 98 GMC sierra and the ect sensor that is on it only had one wire running to it. Obviously the previous owner tried to make something work. I bought a new ect sensor and pigtail to rewire it but can’t find the ground wire anywhere. Could somebody help me with a wiring diagram?
Some ECT sensors have only one wire running to them from the factory. Are you sure yours isn’t one of them?
The ground is probably through the sensor itself so only one wire needed. Check instructions though on whether to use sealer on it. It could affect the ground.
Advanced auto gave me a two prong plug with a two prong pigtail that has 2 wires. This is what it should when looking up my vehicle for a ect at the store. The one that was on the truck did not look like factory. It was a wire soldered on to the back of the sensor. It doesn’t make sense for a replacement part not to fit? Ground wire is obvisouly needed because the sensor won’t work with the ground wire taped off.
This diagram is for the 5.3L engine;
You’re not confusing an ECT sensor with a temp sensor used for other fuctions are you; as in temp gauge operation, cooling fan sensors, etc, etc?
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So is there 2 wires, both a yellow and black wire, in the wiring harness provided for the connector going to the sensor, like in the schematic @Nevada_545 posted above?
I’ll add I’ve had some difficulty in the past with coolant temp sensors, getting the version with the correct number of leads to match my Corolla’s corresponding connector. The manufacturers sometimes switch the configurations around year to year, and this seems to confuse the parts places. Did you take a thorough look at what that part looks like on the Rock Auto web site?
That schematic isn’t useful, in my opinion
No offense intended to anybody
Because the 5.3 liter engine is a much newer design, and completely different, versus any engine available in OP’s 1998 truck. And I know for a fact that the coolant temperature sensor on that newer engine is in a completely different location. Completely different in nearly every possible way
OP’s truck most likely has a 5.7 liter V8 or a 4.3 liter V6. The less common options were the 5.0 liter V8, 7.4 liter V8 and some kind of a diesel engine.
Perhaps somebody could post a schematic for a 1998 5.7 liter GM V8 . . .
I must have looked up the wrong year, here is 1998 GMC 5.7L. Still don’t know which engine the OP has.
Assuming OP has the 5.7, black is ground, but the module does the grounding
Perhaps OP is thinking the sensor grounds externally . . .
Interestingly enough, rockauto shows 2 different sensors. One of them has 1 pin, whereas the other has 2 pins
But I know that rockauto sometimes shows parts which don’t apply
The coolant temp sender for the gauge has one wire, dark green. That one is in the left cylinder head between the first two spark plus.
The coolant temp sensor for the PCM has two wires and is located near the thermostat.
Assuming this is not a diesel engine.
In Summary…
bambsbambino said, “So I got a 98 GMC sierra and the ect sensor that is on it only had one wire running to it. Obviously the previous owner tried to make something work. I bought a new ect sensor and pigtail to rewire it but can’t find the ground wire anywhere.”
" The one that was on the truck did not look like factory. It was a wire soldered on to the back of the sensor."
ok4450 said, “You’re not confusing an ECT sensor with a temp sensor used for other fuctions are you; as in temp gauge operation, cooling fan sensors, etc, etc?”
Nevada_545 said, “The coolant temp sender for the gauge has one wire, dark green. That one is in the left cylinder head between the first two spark plus.”
“The coolant temp sensor for the PCM has two wires and is located near the thermostat.”
We haven’t heard from the bambino since November. He got a truck that was apparently Mickey Moused, perhaps with the wrong sensor. We don’t know which sensor is needed. I see no symptoms or description of a problem, other than cobbled wires/wrong part?
From where I’m sitting, unless the bambino comes back with information, this will remain a mystery.
CSA
I thought babe ruth was the bambino . . . 
The Babe Was the bambino The Bambino.
CSA