I just put an LM7 into my 98 K2500. The swap is going fairly well, but I had a friend come over to delete the EGR, VATS, downstream o2 sensors etc. He said he couldn't see the pcm when he hooked up, but pushing the wires around a bit caused some relay clicking noises, and the fuel pump priming, and then he could read it. Now I have the engine running, but the connection is still very poor and it will die at random at times. The problem is definitely at the PCM. Usually what works best is pushing the wires down towards the ground, onto the pcm. See the photo for what I mean.

I will be building a mount to hold the PCM where it is in this location. I considered putting the Nelson fuse block into the factory fuse block, but it isn't a show truck so I don't think it is really necessary.