[VetteVet]

[QUOTE=coldgin;6090220]I have a 69 gmc 3/4 ton that I have retrofitted tbi injection on the stock 350...out of the blue temp gauge stops working and is pegged to the cold side....I grounded the wire going to the temp sending unit and the gauge pegged to the hot so I thought install new sending unit would fix my problem but the gauge is still pegged to the cold side...only thing I am wandering is the heater hose return hose goes to the pump instead of the radiator like on the late model I got my tbi from...I also changed thermostat thinking it might be stuck open and not letting the engine warm up...any ideas and I very open to suggestions...[/QUOTE

Has the gauge worked since you changed to TBI?

Grounding the sending unit wire shows two things A. the gauge is responding as it should and B. the wire is not open to the gauge.
This leaves the sending unit as the problem. Especially since the gauge was working before.

When you changed to TBI did you mount the gauge anywhere besides the left cylinder head and did you uses any sealer on the sender threads?

The heater hose does not have anything to do with the temperature gauge. You could have the heater hose disconnected and plugged and the gauge would still work.