'86 Jimmy 4in Lift, 40’s, tons, 8.1 Swap- 700r4 said PNNNNN

[ZooMad75]

Something is shorted to ground on that 12v switched circuit. It's the only reason it woul snap a fuse as soon as the key is turned on. Find that circuit at the fuse panel and trace it back by hand. It's touching ground by being pinched or rubbed through to ground or another wire that is a ground source.

 

[campfire]

12v Constant reads 12.5v with the key off. Once the key is cycled on, the 12v constant drops to 10.5v and never comes back up. Is that normal?

No. Either your battery is very weak (and I think we've ruled that out), or some part of the circuit is pulling way too much current (and the supply wire cannot keep up). Pair that low voltage with the blown fuses and you have a 95% chance of finding a short somewhere downstream of that ignition switch.

Under normal circumstances the voltage should not drop nearly that much.

 

[campfire]

Under normal circumstances the voltage should not drop nearly that much.

To give perspective, if you were seeing 12.5-10.5 volt drop at the battery terminal, and you had a healthy 800cca battery, your current draw would be similar to my entire glow plug circuit (10.5 is about what my voltmeter reads when I'm warming). Your wiring harness is probably restricting that flow. Though you did say you're measuring a separate circuit, so SOMEWHERE upstream is losing a couple volts. And your fuse is definitely stopping the flow every time it blows. But that would be a lot of heat if your brand new battery was dropping that far, and it's not normal.

Fuses are your friend, because they make it harder for your truck to catch on fire.

 

[GWeakland620]

Are we sure this distribution block isn’t the issue? Did I wire it correctly?

 

[campfire]

Are we sure this distribution block isn’t the issue? Did I wire it correctly?

View attachment 336297

Do you see a point where the wire(s) could be contacting the chassis?

Side note, if that is the 30 amp fuse that's blowing, your problem is downstream from there.

 

[GWeakland620]

Wiring harness is headed back to the builder. Worst case scenario I’ll buy an aftermarket one and move on.

 

[ZooMad75]

Where does that circuit go? Direct to the PCM? Or does it split off and go somewhere else? With two separate PCM's plugged in and the same thing occurs I'd say it's a short in the wire itself.

PCM's royally zapped by lightening or hooking up jumper cables backward typically won't short out internally quite like is going on here. The fact the fuse pops with the 2nd PCM proves this.

I'd be tracing that circuit. A draw big enough to snap a 30 amp fuse is going to leave a mark where it's shorting to ground it.

 

[Capt Ron]

I'd be tracing that circuit. A draw big enough to snap a 30 amp fuse is going to leave a mark where it's shorting to ground it.

I was thinking the same thing.

 

[GWeakland620]

Well that’s what he is going to do. We’ll see what he finds. He said he has some thing at his shop that finds shorts in the wiring. I’ll hold my breath and my wallet.

 

[campfire]

Well that’s what he is going to do. We’ll see what he finds. He said he has some thing at his shop that finds shorts in the wiring. I’ll hold my breath and my wallet.

Don't be overly surprised if the short only exists when it's contacting your chassis (which isn't in that box). So he may not have anything to find. Or he might.

 

[GWeakland620]

So the harness is still at the guys house. I printed out a pinout diagram from our LKQ Napa account, so we’ll see what he finds.

In the meantime, I decided to replace the other fender. First picture is just more documentation of how rust free this tub is.



New fender on. Great patina. Wish I was doing that kind of build.

 

[beags86]

So the harness is still at the guys house. I printed out a pinout diagram from our LKQ Napa account, so we’ll see what he finds.

In the meantime, I decided to replace the other fender. First picture is just more documentation of how rust free this tub is.

View attachment 337378

New fender on. Great patina. Wish I was doing that kind of build.

View attachment 337379

I wish people didn't think "patina" was an acceptable way to build stuff.
No offense Greg. rant off.

 

[GWeakland620]

I wish people didn't think "patina" was an acceptable way to build stuff.
No offense Greg. rant off.

I’m a believer that it was cool, until people used it as an excuse to be lazy. I don’t mind it, but it’s just not something that would build on purpose. It would be a stage of my build. But not finished.

 

[skunked]

I wish people didn't think "patina" was an acceptable way to build stuff.
No offense Greg. rant off.

Original, straight panels without a lot of rust is not something easy to find therefore I'm not offended by the preservation of those vehicles. However painting a vehicle to look old is played out IMO.

 

[beags86]

Original, straight panels without a lot of rust is not something easy to find therefore I'm not offended by the preservation of those vehicles. However painting a vehicle to look old is played out IMO.

Agree on the painting patina on.
I guess the whole rat rod and freiburgers ratty muscle car thing is just played out to me.
I have no problem with dragging a old pile of shit out of the field and put it back on the road. And even driving it for a few years with "patina" but the second you clear over it and Decide to keep it. I'm done.

I guess growing up I saw an old car, that was restored, I thought that's cool.
If I saw a running driving project, I also thought it was cool knowing that someday it was going to be painted and done.
Then this shit started.
As you mentioned, I can respect finding panels that are clean and not rusty/dented.
But I can't appreciate a car that wasn't "done" when it was "done" if that makes sense.

 

[imiceman44]

I wish people didn't think "patina" was an acceptable way to build stuff.
No offense Greg. rant off.

I don't do patina for a build, but I don't mind driving a vehicle that has patina.
I just don't believe in making that because the same effort can produce a nice looking paint job

 

[GWeakland620]

Getting the harness back today. He said he had a couple pins swapped in the wrong area. We’ll see if we can hear some vroom vroom noises later today.

 

[imiceman44]

Getting the harness back today. He said he had a couple pins swapped in the wrong area. We’ll see if we can hear some vroom vroom noises later today.

That happened to me when I was swapping engines in my freightliner.
Bought a brand new ecm harness and it wouldn't fire.
Turns out 2 pins were swapped, one was the power to the injectors

 

[GWeakland620]

Still fighting a ground issue. Magic short finding wand is coming out next.

 

[GWeakland620]

I’ll try my best, as I don’t know what these go to.

The plugs are both powered and grounded. We had no idea. Pulling the harness apart to get rid of these plugs and fix the grounds. That should take care of the issue. Should be putting the harness on tomorrow.