I had some work done to my car and when I got it back my temp gauge no longer worked. If it is simply just unhooked where can I look to reconnect it? Or what else can render the temp gauge to not work? Thanks in advance.

 

Look on the driver side above plugs 1&3 for a single green wire hanging loose. It attaches to a brass fitting that is the guage sender, probably came off during servicing. It's fairly common especially if the plugs were replaced.