It's an 88 base camaro. Was a 305 tbi but it's a different and carbbed engine now.

I need a coolant temp sending unit to plug into the 1\4 inch (back) hole on my manifold, but when I went to go buy one, the Autozone guy swore up and down that the sending unit that sends to the gauge is the single-wire one, which happens to only come in the 1\2 inch. I thought for sure that the single-wire sending unit went to the fan and the two-wire sending unit went to the gauge.

I can't just check because I redid 100% of the wiring in the car. So, which sender will send to my stock gauge cluster? (I'm gonna wire the gauge cluster in manually as I have no computer anymore.)

Gauge sending units are available in 3/8" (newer heads) and ½" (older).

That SU doesn't go in the manifold; it goes in the driver's side head between the #1 & #3 plugs.

The fan switch goes in the same hole in the pass side head; between the #6 # #8 plugs.

If you're not using an ECM, you just need a pipe plug, or a heater hose fitting, in the various intake manifold water holes.

I don't want wires coming out of my heads, so I'm gonna put the sending unit at the back of the manifold, I just need to know which sending unit talks to our stock water temp gauge in the gauge cluster. The single-wire sending unit or the two-wire sending unit.

SINGLE WIRE. thermistor. blade style connector.

Thanks.