Today my temp gauge started jumping erratically. It liked to read below 100* down the highway, seemingly jumping 30* with the beat from the sub. No relation there, just thought it was funny Whenever I'd come to a stop though, the needle stopped bouncing and slowly moved up to temp.

Anyways, on to my question. Is this a bad gauge, temp sender, or wiring? Or something else entirely? TIA

 

Could be any one of the three. Can't pinpoint it without some diagnostics on your end. The first thing I would check is the connector on the sending unit located at the back of the head on the driver's side. Is it loose?

 

My 97 was doing this.......I cleaned the connectors to the sensor and that solved it for me