Electrical problem
1987 Chevy Blazer 6 cyl Four Wheel Drive Automatic 260000 miles

I just bought a '87 Chevy s-10 Blazer 4X4 2.8L. It is in fine mechanical order, but the electrical is all screwy. For some reason when you click the blinker on, the proper turn signal works in the front, and so does the yellow running light on the other side of the truck. But on the back, both lights flash like hazards. The brake lights work fine, but when the lights are turned on there is no difference. i took the bulbs out of the light covers, and it seems one bulb is operating as both the brake light and the regular lights. there is a small bulb that does not work on either side of the rear. This is all very confusing to me. I took off the steering wheel and examined the blinker assembly but that seems to be fine. What could cause all of these problems? I took apart the whole truck almost, and all of the wiring seems to be untampered.