Hello everyone! been trying to find answers to my problem's using this site but have not had any luck thus far. Im sorry if this is in the wrong forum but I can't post any where else.
I have a 2001 chevy blazer Vin model W. with the 4.3l V6, 4x4. auto trans.

I bough this a while back, shortly after I got it i found out that it had bad engine problems (knocking and metal in the oil). So My wife and I decided to do an engine swap in-steed of waiting for the motor to blow a rod or lifter. So we went and picked up a used 90K 4.3l and did the swap at a friends house. Was kinda a pain but got it done and was running amazingly. After the swap i got about 2500 miles out of it before i hard more problems. Went to go fishing and got in the SUV , Started fine, got half way done my road and it just died. No dimming of lights or anything of that nature just instant shut off. Managed to get it back on and home , then it continued to not start. So did some research n replaced the ignition switch that did nothing. So went and pulled started n cleaned up all connections and had it tested, it failed so i bought a new one. Put that in ( with cleaned connectors n yes everything is tightened down) Still nothing. What I mean by nothing is that, on turn key there is no crank or start, i get dash lights and radio and all that stuff but when i turn the key they shut off and no crank no start. So went out and got a NEW battery, Still no crank no start. Had my uncle use his multi meter and we are getting power to alternator,battery and ground. Also "bridged" the starter with some wire and when I did that it tryed to start the engine but would not ( key was in ON position), it was acting like something was stopping it from firing.

Also found a set of wires that plugs into a black sensor looking box on the shifter under the boot ( floor auto shift) that had broken wire. Went to junk yard and got a matching plug and spliced the new one in (yes the right way). All this seemed to do was let me take my key out ( yes I had not been able to remove key without hitting the emergency release button in the cowling on steering column).

Sorry about the long post and if this is in the wrong spot but like I said I cant post any were else and I need to get this running for my Family of 5. Any help and info would be Great!!
Thanks,
Justin Silver