One temp sensor for gauge and PCM
 

***I tested this on my 68. It should work for all 67-72.***
I've heard it also works fine on square bodies and newer. I'll probably do it to my 93.

If you don't want to drill your head for the stock gauge sensor there is another choice. A 98 F-body 3-wire sensor will send the proper signal to the PCM and your gauge.
It is a TX111 sensor and PT2319 connector. It threads into the current ECT sensor hole and you just need to add the connector pigtail. Pins A&B tie into the original PCM wiring and pin C goes to the green wire in your truck harness.

The temps may seem hot, but these engines run hot by design. Stock 04 Vette low fan speed comes on at 226F, high at 235, and GM calls 260F hot.

Here's some pics in reference to temperatures. Sorry for the up/down ones.
190F, 212F, 228F (fans just came on), and 260F (simulated with a 55ohm resistor)

Re: One temp sensor for gauge and PCM
 

I did play around with the calibration resistor on the back of the gauge, but the stock 90ohm one gave the best overall result thru the usable range of the gauge.
I attached some diagrams. Pin C is the one you tie in to the green wire in your original harness. A&B are tied to the PCM wiring.

Re: One temp sensor for gauge and PCM
 

This is some excellent information.
I guessing the newer sensors are more accurate because of the required computer inputs are unlikely to put up with the +- 10% of the old analog stuff.
Purchasing the sensor is the easy part. Finding the proper pigtail may be a bear.

I got tired of looking at the faded red when all the other gauges were bright. So I ordered an NOS temp gauge through eBay.
It arrived today. It was under $60 delivered. It came with the resister in a separate envelope.
They are reproduced but the cost was only slightly less and sometimes more than the NOS part.
Some of the reproductions had AC and MADE IN USA ON THEM. Some did not.
I also included pictured a re-pop with out the identification and the gauge black background looks to flat to me.
I was also suspicious when both gauges a read differently disconnected.

I used an adapter to connect my sensor to the LS motor. I was concerned it would not read correctly but it works great.
Cheers

Re: One temp sensor for gauge and PCM
 

Nice looking gauge. I forget how red the hot zone is on these when new.

The connector and sensor are available and in stock most places
TX111 sensor and PT2319 connector

Re: One temp sensor for gauge and PCM
 

FYI that pigtail is the same as many other pressure and temp sensors, if you have the means to crimp them correctly, the connector is pretty cheap.

https://www.ebay.com/itm/164155550625?_ul=IN

https://lowdoller-motorsports.com/co...ressure-sensor

Re: One temp sensor for gauge and PCM
 

Thanks for the link. $2.50 is inexpensive.
Using google search I found them for as much as $45.00.
I could purchase 18 of them for the same price.
That link is a keeper.

Re: One temp sensor for gauge and PCM
 

no problem, the lowdollar stuff is pretty good quality, i use it on all my own builds.