Turn signal won't work
Drivers side turn signal/brake light in rear on my f-350 won't work. The bulb works (replaced) and using a go-no-go checker the light flashes in sequence with the signal.
When you say the tester is flashing in sequence where are you connecting your tester? If all the lights work except the left rear one I would look at bulb socket first then look at connector and wiring.
Same prob here . Ever get it fixed?