Two ECT Sensors LS1 Where is the other one?

[Corveric]

We have transplanted an LS1 from a '98 Silverado into a '97 (originally was a 4.3) and we used a computer and harness from an '00 Vette LS1. (Or so i am told)
The harness has two engine coolant temperature sensors, a multi wire that goes to the driver side head, and another single wire that is somewhere around the back of the engine on the driver side. With the engine in, there is no room to get one's head down there to look.
Can anybody help us find the sensor that ought to be there?
There is also another sensor which hooks up to the electric fans which is all looked after. I believe that the one we are looking for will operate the dash board gauge.

[VetteVet]

I'm no expert on the newer engines so I did some googling and I read that the ECT comes in a two wire and three wire type. The three wire is for the older engines and the gauge wire ( usually green ) comes off it and is for the temp gauge.
The wire in the back may not be for an ECT but for a cam position sensor which is located on the rear of the block at the cam.

[Corveric]

So perhaps, since we have a newer wiring harness and an older engine and the repair is to replace the current 2 wire sensor in the head with a 3 wire sensor and splice our stray ECT wire from the back of the engine into it. That would certainly answer the issue. I have seen that there are two and three wire sensors but I was not aware that the extra wire was for the gauge.
I will try it and post the results.
Thanks for the help VetteVet, a small piece of missing info but it may be the key.

[clinebarger]

Theres not two ECT sensors on any gen III engine the PCM sends the temp signal through a serial data line to the insterment cluster in a stock app.

The wire you found in the vette harness is probably the oil temp sender plug no other apps had this exept the vette.

[68 short step]

Originally Posted by Corveric

We have transplanted an LS1 from a '98 Silverado into a '97 (originally was a 4.3) and we used a computer and harness from an '00 Vette LS1. (Or so i am told)
The harness has two engine coolant temperature sensors, a multi wire that goes to the driver side head, and another single wire that is somewhere around the back of the engine on the driver side. With the engine in, there is no room to get one's head down there to look.
Can anybody help us find the sensor that ought to be there?
There is also another sensor which hooks up to the electric fans which is all looked after. I believe that the one we are looking for will operate the dash board gauge.

in some late model 99 silverado's they had 5.3/4.8/6.0 engines (in the LS family), but in 98 they didnt come in trucks....as for the temp sensor, there is just one position they come, and thats the driver front... the wire colors are yellow and blk...the oil press. wire color typically is tan...
i hope this helps ya

[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.