Installed a Champion aluminum radiator with my LS1 swap into my '91 3rd gen Camaro. The relay kit includes a thermostat switch who's sensor end is too large for the hole in the intake just beneath the alternator as shown below. (1) is there another ECT senor on the LS? (2) anyone know of the correct part that will fit? (3) can I just "tap" into the current ECT pigtail? If so which wire (I believe the pigtail has three wires)? Thank you!
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1. No
2. I don't; doesn't mean there might not be one though.
3. No. And not that it matters to the issue at hand, but the stock CTS has 2 wires as your photo shows, not 3.

A "switch" is just that: a switch. It's a mechanical contact set, which in the case of a fan switch, the contacts aren't contacting when it's cold, but then when it gets hot, they make contact, thereby turning on the fan. A [mrspock]"sen-sore"[/mrspock] is more often a continuously variable resistance, more like a thermometer than a "switch". That's exactly what it is in this case. Needless to say they are not interchangeable and not capable of both being hooked to the same wire without one affecting the other and causing completely incorrect operation to both systems.

You can't do away with the coolant temp sensor in the head (head, not intake), and you can't just randomly hook some switch to either of those wires and have everything do what it's supposed to. Don't even think about messing with it.

Best thing to do would be to simply get the set of stock LS1 fans that went with the engine you got, along with their stock wiring, and install those; then use the stock ECM's existing capability to operate them. But if you just really want to do some extra work and go to extra expense by fooling with all that aftermarket crap, you could either: get one of those switches that pokes into the radiator; or, find one with the same thread as the stock CTS, and put it in the same hole in the other head, which would be at the rear passenger side. It's just a SWITCH, after all; no contact when cold, contact when hot. About the only variations would be the current carrying capability (which since it's allegedly driving a relay, wouldn't matter), the thread size, the electrical connection to it, and the temperature it switches at. The hole in the heads is some metric size, straight-thread though not pipe like the aftermarket one you have there, but I don't know offhand what thread it is. The google might know, though. It knows everything.

 

Thanks sofakingdom...above you said, "...CTS, and put it in the same hole in the other head, which would be at the rear passenger side."...did you mean front passenger? My picture above shows the CTS just below the alternator. If you are thinking rear, then maybe the answer to my 2nd question is yes?!

 

LLLLOOOOOOOKKKKK at the heads. Imagine 2 of them sitting on the ground in front of you. Remember that the castings ARE IDENTICAL IN EVERY DETAIL. Imagine you have both of them laying there facing you with the exhaust flange showing.

OK... the CTS hole is at the left of the one you're about to bolt up to the driver's side, eh??? So, ... where is that same hole on THE OTHER ONE????

At the LEFT END as you're LLLLLOOOOOOKKKKing at it, no???

Which when you bolt that one up to the pass side, ends up at the rear.

 

And yes, there MIGHT be a part that gives a "yes" to your #2; doesn't necessarily mean that it's a "better" option than using the stock stuff you ALREADY HAVE. Just because you CAN DO a thing, or that a part is "available", doesn't necessarily mean that it's automatically A Good Idea.