Temperature gauge is not working

I have a 1996 Jeep Cherokee, 180,000 miles, 4.0L engine, 4WD. I replaced the engine on my Jeep with an engine from a 1997 Wrangler, 4.0L 75,000 miles.

Everything went okay, the new engine starts and runs good, the car drives. The only problem is that the temp guage does not work. The needle stays at the left on the 100 degree mark. I replaced the thermostat but that did not make it work.

Then I noticed that the 1996 block has an extra coolant sensor in the top of the head near the firewall on the drivers side and the 1997 block does not have this sensor. All other ports and connection locations were the same on the 2 engines. So I have that one connector disconnected.

I am guessing that the 1996 computer used data from both sensors to make the temp guage work.

What can I do now to make the guage work aside from drilling a spot in the head to add the missing sensor?