Temp gauge not working

I have a 92 F/S originally a 4.3 5 speed truck. i have put a 6.0 in it and got an adaptor from street and performance for the oil pressure and water temp to use the original sensors from the 4.3. I am trying to use the original gauge cluster, the oil pressure gauge works, but my temp gauge isn't. All of the 4.3 wiring is still on the truck. There is a yellow and a black wire going to the sensor, the yellow is supposed to have 5V, but when i tested it, it didn't. Was just wondering if anyone had any ideas?

You checked the voltage with the key where? Also odds are if the coolant temp sensor is a 2 wire it's the ecm signal. Gauge coolant temp sensors on those years should be a one wire.

I'm not familiar with that harness, got any pics?

I would have to agree with marcus it sounds like you are trying to use the coolant temp sensor not the coolant temp switch which should only have one wire and it should be green. I have the complete 92 gm service manual if you need the diagrams for your truck.

I found the one wire sensor, it is necessary to use both the coolant temp sensor and the gauge sensor?

Yes