Cessna 310 pilot reported a faint electrical odor while flying at cruise altitude; resulting in a return to the departure airport for an uneventful landing. The electrical anomaly was later attributed to a faulty fuel gauge.

Narrative

I took off from ZZZ for a second survey lift in the area. Upon leveling out in cruise my camera operator mentioned that the area was bad for imaging so we started our way towards our next project in City X. While in transit; a controller that we had just been handed off to said that he was not receiving our ADS-B but was receiving our Mode C. The controller requested I reset the transponder so I restarted it using the buttons on the device (not via circuit breaker). After resetting the controller mentioned that there was no change.While in the process of the reset I started smelling a very faint electrical burning smell; almost immediately after I noticed my camera operator mentioned he smelt something as well. Upon this recognition I started reducing electrical load and contacted ATC to make my way back to ZZZ. Not long after; the smell had slightly intensified and my operator mentioned he could see a light haze of smoke in the cabin. We requested priority handling and I continued inbound for Runway XX @ ZZZ. When nearing ZZZ the smell and sight of smoke lessened while I continued to make an uneventful landing. Once clear of the runway the fire department did a brief lookover of the exterior and we continued taxiing to the FBO. After parking I did a deep lookover of the aircraft and was unable to find a visible source of the burning.After speaking with management and different maintenance facilities I attempted to recreate the issue on the ground by loading up the electrical system. This resulted in the right fuel gauge circuit breaker to pop.