Junction Block Explained...Plz!!!!
 

After a few hours using the search function of the site I'm yet to find a clear explanation of the purpose of the junction block an the wires that go to it. You know the diamond shaped plastic thing-a-mo-bober :lol: on the fire wall.

I spent the better part of an hour earlier today holding the wire harness from an 86, V8 Gas truck in my hand and a good half hour on the wire diagram found here: http://www.73-87chevytrucks.com/tech..._V8_engine.jpg

seams to me like it one big power loop, can some one please explain/elaborate/confirm the following to me:

1a)Post A of the block has a wire that goes to the bolt that sticks out of the alternator. I'm assuming power flows from the alternator to the junction block?

1b)Spliced in to that wire is a wire that goes back to the fuse block, Im assuming this brings power to the fuse block while the alternator is turning?

2a)Post B of the junction block has a wire that goes to + post of the starter were the battery cable goes, I'm assuming that it brings power to the battery to keep it charged?

2b)There are two other wires spliced in to that + post of the starter. ONE goes back to the fuse block, Is that how the "ACC" setting on the ignition switch powers stuff like radio, power windows, etcetera?

and the SECOND one goes to a plug on the alternator next to the brown wire that i understand is a signal wire for the Amp meter in the dash.

Re: Junction Block Explained...Plz!!!!
 

I could be wrong (just ask my wife, LOL) but I believe the junction block is a way of including "Fusible Links" into the engine side of the firewall. The block would allow you to change a bad fusible link without removing the harness.

http://en.wikipedia.org/wiki/Fusible_link

http://www.madelectrical.com/catalog/fusible-link.shtml

Re: Junction Block Explained...Plz!!!!
 

Mine has two that goes back to the fuse block (one powers the gauges )and on the other side of it, one goes to the alt. and one to the blower motor power and one goes to the alternator or starter, not sure

Re: Junction Block Explained...Plz!!!!
 

Its just a junction block. All it does is tie all those wires together. I assume it was just an easy way for GM to add on additional circuits and like S10 fan said, if a fusable link was blown the individual harnesses could be swapped out with out cutting splicing in a new one. I think maybe its the way the block looks that has so many people intimidated into thinking its more than it really is :lol:

Re: Junction Block Explained...Plz!!!!
 

Ok, that part about being able to swap out a burnt fuseable link did not occur to me, and it makes much sense. But what about the current flow I listed? Is that correct?

Re: Junction Block Explained...Plz!!!!
 

As far as I know everything you have listed is correct. I dont know off the top of my head if one wire going to the fuse box feeds 12V constant and the other ACC but together they get power into the cab.

Re: Junction Block Explained...Plz!!!!
 

only one way to find out right? unplug one at a time :lol: looks like i will have to try it on my truck. yawl take a seat cause its gonna be a while I'm in the middle of redoing my fuel lines and exhaust all over again :metal:

if any one else knows for sure feel free to let us know.