I changed out the fuse block on my 2010 Suburban 5.3. The one that's on the front drivers fender well. This is because my back up lights were on all the time - key on or off - in any gear including park. It seemed the relay is inside the block so it seemed like an easy fix. I bought a used block assembly that had all the fused and relays intact. Everything worked except it would not crank. I checked all fuses and put all my old relays into the new (used) block. It still would not crank! So I bought another fuse block and it does the exact same thing. Is there some ecm reset or something I need to do? Thanks!
PS: When I install the original fuse block back in it cranks and runs fine.

 

i have installed lots of these. the only thing I can think of is some times the harnesses under the block come out. make shure there all in place.