Just bought a Tahoe limited (2000) when I start the car my top outer lights come on then when I switch my side lights on all 6 lower ones come on , when I turn switch to low beams nothing changes & I can not get high beams. They are after market lights but all the connectors on the back of them match up any ideas???

 

I am not sure that I fully understand your question. Exactly what lights are you referring to (parks/corner markers, DRL, low beams and high beams)? What are the "6 lower ones"? We need to know what ones you mean.

I wonder if the previous owner has installed diodes somewhere when he did the after market lights, which is also a common modification.