'97 Chevy Tahoe

We have a '97 Chevy Tahoe that we are trying to get on the road. The provious owners had installed a radio with an incredible amount of wiring which we have removed. The signal lights were not working but after checking fuses and bulbs we have been able to get all signals, reverse light, and hazards working. Now we are struggling with the brake lights and the middle tail light. They have never worked and we have check all fuses and bulbs. We even replaced the brake light switch. Any thoughts as to what we can try next. We thought that there should be a relay for the brake lights but were unable to locate one in the truck, the manula or at the part store.