Gen III harness has a short somewhere

[74kay5]

I have a 6.0L 4L80E swap in my K5. 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.

 

[dyeager535]

So if I'm reading it right, you blow a 20 amp fuse, and that circuit is fused AGAIN on the speartech harness, but the truck fuse panel is the one that typically blows?

 

[1979jimmy350]

did you use rubber grommets on all the wires that you passes through the firewall? If i were you i would disconnect the PCM when trying to find the short to prevent frying it.

For my ignition wires i have fuses for each o2 fuel pump realy etc. are you saying you are running all of these off one fuse?

 

[rufusbooth]

I am no expert here but the troubleshooting method that you have chosen seems to be viable you just need to take it to the next level.

In the harness I built for my lq9 I have individual fuses for each item in the harness. In this case it sounds like you are running everything through one fuse. That is probably not the best method of circuit protection but that is a subject of another thread.

To continue troubleshooting I would continue down the same path you are going by disconnecting everything from the harness. Get the rest of the injectors etc. If you have "everything" disconnected from the load side of the harness and you still blow the fuse then you are most likely going to need to blow apart the "15 wire" bundle. once that is disconnected replace the fuse and start connecting the "15 wires" one at a time until the fuse blows. Then trace that wire down and find the short.

Not the ideal way to troubleshoot but without individual identifiable power runs it wont be an easy one to troubleshoot.

Rufus

 

[dyeager535]

If it's blowing fuses with everything disconnected, "all" you need to do is start at the connector end (whichever sensor, etc) and check continuity to ground on each of the pink wires.

 

[74kay5]

Here's an update. PCM was unplugged a long time ago in this process. The fuses are doing their job so I'm not to worried about the speartech setup. Although I might actually be able to start the damn truck if all the IGN wires were fused individually. I have 3 fuses Fuel, IGN, and Battery. Anyway I kept unplugging things until it got to the point where almost everything was unplugged so I just said **** it and yanked the whole harness out. I noticed that the length of wiring that goes back to the tranny was stuck. When I was driving it I was on a really rough road and the harness must have got wedged in between the transmission housing and the body. As the body bounced back and forth sawed the harness a little. Sure enough I can see one of the pink wires is damaged a little. I'm going to hook up the ignition power to it with the harness away from the body and see what she does tomorrow. If that doesn't work then I'll have to pay that $300 fine to the city for being parked in front of my own house on what the city code enforcers are calling a sidewalk (that's actually my driveway).

..................And then I'll have to set the blazer on fire.

 

[bryanspeed1]

i am having a similar problem did you ever figure yours our?