Recently I've inherited a 1987 K5 with the 350 TBI and TH400. It's important I finish the build my dad started. But I'm out of my depth in a lot of ways. Any help y'all could give would be greatly appreciated.

The wiring harness my old man put in is one of those after market ones that is supposedly for this particular vehicle. There is a 30A fuse that blows immediately when I connect the battery terminals. It says Power Accy. So clearly something is grounded out somewhere but I have no clue where to even begin looking. I'll put in an image below. The blown fuse is the one with the red LED.

If anyone has any suggestions of where to look, I'll be in your debt.

Also, the horn works, AC works, power windows work, cigarette lighter works, none of my cab lights even have bulbs but the under the dash light that's connected to the headlight switch works. The gauge lights work. I've got no radio or speakers installed. I've disconnected the lights on the grill guard.

Again, any help would be awesome.

 

It has a big fuse that’s silver in that slot. Idk if that matters.

 

I couldn't spend a lot of time this morning looking through the wiring diagrams I have to see what might be on that circuit from the factory, but you should have those same diagrams so I would also review those to see what you can come up with. There aren't a lot of full-time battery powered circuits in those trucks so it shouldn't take much to figure it out. I would bet that it is something added on that is causing the problem. You could also try tracing all of the wiring that connects to the face of the fuse block up at the top that you can see in the image. Perhaps try labeling them all, noting their positions, and disconnecting them, then see if the fuse blows with them disconnected. This could also allow you to narrow down the source.

 

Hey y’all, so I took your advice and started trying to figure out how to read the fuse block and wiring diagrams. Not as complicated once you get into them.

*Tip: they are extremely confusing when you look at the whole picture! But, I found that if you grab a ruler or highlighter, anything that can help you trace or focus on one part at a time, they become a lot easier to understand. Just focus on one piece at a time and trace one line at a time. It also helps to pull up a key online that tells you what each of the diff symbols mean.*

It turns out that the Power Acc circuit in the fuse block, for almost all vehicles ever, is what is used to run power seats, power mirrors, power antennas, seat warmers, rear window/mirror defrosters, and power door locks. Sometimes, it is also one that a lot of back yard engineers and shade tree mechanics will use to power things that need to always be hot. Like after market fog lights, etc.

Well, in my case it’s the aftermarket fog lights and the door lock actuators. The reason it keeps blowing the fuses, or making the circuit breakers get super hot and burn out, is because it’s grounded out somewhere. So today I’m gonna trace all of those lines and see where the issue is.

I’m hoping it’s just the door look actuators, but there are a lot of unexplained wires all over that truck!

I’ll keep everyone posted on what I learn. Also, thanks again for all of y’all’s time and help!