cursor,curses,whatever.....lurkin my Arse
Steve,the diagram that Stuart gave you is right on.
The Actual connector if you have not found it yet is on the firewall, just below and to the pass side of the main harness. about the size of a silver dollar.
Unplug this and test out the different spades showing,there will be 4, Lt sig, Rt sig, Running lites, Stoplites.The Round connection plug head on will look something like this.
_ _
! !
The exclamations should be solid vertical lines direct under the center of the flat line, but you get the idea,DONT You

If all test out fine,
Then reconnectthe plug and test the wires at the juntion block at the rear crossmember and left framerail,should still be there unless eliminated by a prior butcher, Ahem owner for a prior short.
If All 4 test clean,Same test process of elimination,Now you know that you have juice to the back and can see if it is a bad ground or a bad socket/worn bulb.
Hint{an alligator clip jumper wire from the socket to a GOOD ground does wonders!
WATCH Out Stu might oughta wanna paint your house for that Diagram
Cheers,Good Luck,and Regards