Tail Light Problems

New to the forum, so Hello All.
I have a 99 Tahoe with 2 back doors. The blinkers has quit working. A few weeks ago the right blinker was double timing, which used to meant the bulb had burned out. I pulled the light assemblly out, checked the bulb, but it hadn't burned out. swapped bulbs and all 3 bulbs worked in any slot, except the blinker plug. i even changed the light assmebly, and it didn't solve the problem. I eventually found that the copper contacts between the body & the door had to be cleaned. Now, both sides have started doing the same thing. the running lights burn, the brake lights burn, but the blinkers don't blink. i have checked all the fuses, new bulbs, plugs/connections, everything that i know to do. what else is there? is there another plug along the frame under the body that i haven't found? or another plug inside the body besides the on plugging into the lamp assmebly plate? any help would be great. i am at a loss, and a ticket waiting to happen.

thanks.

The blinker relay may have burned out. If I remember right, a 99 Tahoe is still the old body stlye, so the relay should be under the drivers side dash above the parking brake. There's a small electrical center there that contains the module that makes the 'chime' noises, possibly the day time running light relay and the blinker relay. There is probably some other stuff there to. I'm not sure which relay is the blinker one. You could reference a Chilton's manual.

Hope this helps.