Turn signal has rapid flashing on dash when left turn is selected bulb working

check the front bulb(left side),look close,one of the two elements probably burnt out

Left side brake light working ok > with headlights turned on? .. Likely insufficient ground circuit at left front or left rear bulb socket.

I had same issue and resolved by slightly bending copper contact out a half millimeter or so. There are three contacts, but the silver colored ones looked OK, but the copper one was depressed a bit.