I have a 6.0L 4L80E swap into an older 4x4 K5 Blazer. Been working awesome for years. Running a custom PCM and harness by speartech. Made some changes lately, installed long tube headers and new full exhaust, moved PCM and tac box, the fuel pump relay and 3 fuse block inside cab. I took it for a spin after that and everything was fine until I hit a bunch of bumps in the road then it died. Noticed that the check engine light wasn't comming on when I turned the key on....20 amp ignition fuse was blown. Replaced it and as soon as I turned the key, blew again. Jiggled wires and replaced the fuses until I ran out and had to get towed home. Been troubleshooting all damn day and does it no matter what. It's usually the 20 amp on the K5 fuse block that blows. I have the ignition input wire on the 6.0L harness plugged into the ignition input slot on the K5 fuse block. It's always been fine this way.

The 20 amp ignition fuse on the speartech harness will also blow occasionally also. The ignition fuse has a single pink wire that goes to a splice that connects to about 15 other pink switched ignition wires on the harness. Disconnected the PCM, fuel pump realy, TAC box connections, MAF, injectors on the drivers side, o2's tranny connector, and a bunch of other connections and same thing. Fuse immediatly blows. Don't even get a fuel pump sound or noise comming from the throttle body. It's like one of the ignition wires is stripped bare and resting directly on bare metal but I've checked all the places where the wiring goes through the firewall and nothing seems to be stripped. I've carefully inspected all the things that I changed around recently and they all look fine. I have a pile of electrical tape and loom that I stripped off and removed to search. Problem is somewhere in that mass of pink ignition wires but I can't find it by looking at the wires. Any other way to find the short? I have to find the problem soon, the truck is parked in a place where the city is going to give me a $300 fine unless I get it movable soon.