Technical One stop light not working

[NeverRacedOrRallied]

Our Fiat 500 Lounge (2013 on a '63 plate) was reporting a stop light fault. Checked and found rear passenger side bulb not lighting up. Got a new bulb at the weekend, it made no difference. Put the "failed" bulb in the other side and it lights up, bulb is fine.

There is no obvious corrosion or other fault on the pins on the connector. Connecting the offside tailight cluster to the passenger side replicates the fault - the brake light doesn't light up. It's getting a low voltage, about 3v. Husband says there's a shared earth and everything else is working so he doesn't think it's an earth fault.

What else could it be? Currently he's taking the back seats and panels out to try and trace the fault back up the wiring. Any ideas would be appreciated, thanks.

 

[Mike1alike]

Currently he's taking the back seats and panels out to try and trace the fault back up the wiring.

Yes, that is good approach. He surely will get to it.
One useful thing he can do: safely have a wire connected to battery and other end to the stop light. And test both lines. Wire on battery (+) terminal used with stop light ground. Measure with multimeter and/or connect the light bulb to it. Then the other way around, cable on battery (-) terminal and use stop light (+) connector. That will tell if ground or (+) line is faulty on the stop light.

 

[Mike1alike]

And also, Welcome to the forum!