I am confused about which plug is for my engines coolant temp sensor. There are 2 plugs that look likely. I have a b17. The stock harness that came with it was not on the engine when I got it. I have the haynes manual but I am still not sure. Here is the first one.
And the second one to the left of the first on the backside of the engine... TIA

 

The first pic is the actual engine coolant temp sensor. I believe this is where your ECU measures your coolant temp. The second plug, if its on the t-stat housing is the fan switch. I used it when I did my B series swap on my car. You take your fan switch wires and then wire em up to a plug and then plug it into that female sender on your t-stat housing and viola you have a fan switch. Have fun with the swap.

O BTW. Good first post. Detailed enough and easy to understand and pictures to boot. We dont get that very often here on HT.

 

Thanks Blaze. There is another plug I've found. Its a green one next to the oil pressure sending unit. Here's a pic...TIA

 

I think that the green one is your knock sensor... Not positive, but pretty sure. Try the knock sensor plug and if you get a CEL for the KS then you know that that isnt the right plug. The other sensor with the singe post is your oil press. sensor. Good Luck.

Blaze