My 98 GMC has a brake light issue, the left and right brake light, rear turn signals fail to illuminate.

* The 3rd light or overhead brake light is operational.
* The Headlights and front turn signal flash.
* No blown fuses.
* installed new bulbs(turn, park, and brake),no change in status.

any ideas ?

 

You need to replace the combo switch (turn signal switch). The left and right brake light go through it. The high mount light does not which is why it still works.

 

is the combo switch the the same as the turn signal/dimmer/windsheild washer switch on the steering coulmn ?

 

Yes it is.