Is the tail light on that side also out? If so, it's most likely a bad ground. If not, be absolutely sure that the bulb is good first The brake light and turn signal work off the same filiment within the bulb, and use the same wire to the back for both functions. If all that is good, check the connector to your multifunction switch (the one you described) and if the connector is looks good, try testing the brake light/turnsignal wire there for power with either the brake pressed, or the turn signal on. Don't remember what color the wire is, but it's the same as at the light. If there's no power there, then replace the switch.