The story:
I just bought this Blazer ('95 4.3L). The guy I bought it from said he just put in a new Coolant Temp Sensor. This is the style where it is on the driver's side of the block. It appears there are a lot of differences between model years, with regards to this sensor, and I'm confused about my exact setup. Can anyone help straighten this out? Do I have two coolant sensors, or is the one in the drivers-side block for the gauge and PCM? I don't see any other sensor in the intake manifold, near the thermostat housing, or anywhere else.

The problem/question:
The guy I bought it from installed a new sensor with a two-wire plug. The problem is, there was originally only one wire going to the original sensor. The way he had it wired, was he wired the two wires from the new sensor, to the 1 wire going back to the PCM. So, as one would expect, the Coolant Temp Gauge did not work. So, I tried using a little common sense, and took the black wire from the new sensor, and grounded it to the block, as the wiring diagram in the Haynes manual says that the black wire should be a ground. Then, I go to crank it up, and am pleased to see that the gauge appears to be working. The problem is, the gauge continues to rise and rise, to a FULL TEMP OVERHEAT!!! Is this because I was supposed to use a one-wire sensor, and by grounding the black wire on the two-wire sensor, I have completely messed up the indication? Or, should I be worried about an actual overheat? What can I do to correct this situation? THANKS!!!

Edit to above: After more digging around, there is indeed a second coolant sensor buried where I didn't initially see it. It is near the thermostat housing. I think the guy I bought it from put the wrong sensor in the wrong spot? Does this sound about right?

 

The single wire sensor for the gauge cluster should be in the cylinder head. The two wire sensor for the PCM should be in the lower intake manifold near the t-stat housing. It sounds like the previous owner installed the wrong one in the cylinder head.