94 Astro- Eng temp reads cold

Wife was driving. Noticed engine running rough. Noticed temp gauge reading "hard over hot"...but kept driving?!! 'til she was at private mechanics' shop where engine made clanging sound then stalled. Mechanic found lower rad hose disconnected. He reconnected hose with new clamp and filled system with coolant.
Engine now runs very rough, check eng light on and temp gauge reads cold although engine seems hot. I replaced Engine coolant temp sensor...No effect. Measured +5 VDC @ sensor connector which suggests sensor getting power from Eng Computer but senor doesn't seem able to get signal to gauge. Schematics I have in "Haynes" manual don't really give good description of circuit. (+5VDC from ECU to sensor then signal goes back to ECU ... black wire and yellow wire. Don't know where connection to send signal to gauge on dark green wire is, and not sure which dark green wire on which connector of instrument cluster.)

I'm replacing thermostat thinking that maybe it's stuck closed ... but I really don't think it's the problem. (easier than replacing water pump)

Anybody know where I can get wire harness drawings or have any other suggestions?

when it overheated it probably wrecked the thermostat so it is stuck open. it also probably blew a head gasket since it running so rough. the wire with 5 volts is the feed wire the other goes back to the guage. do a compression test and find out if you blew a gasket or not. if you have a 12 pin aldl below the steering wheel jumper a to b and check your engine codes.