Why did GM bury the 4 wire power distribution junction in the harness?

[snipepod]

As part of my 1976 K5 restoration, I am replacing my 70amp 12SI alternator with a CS144 140amp unit. I need to upgrade my wiring to get that added power to the proper spots. I have removed the engine wiring harness and cleaned it up as part of the restoration. It gave me the opportunity to strategize on what wires need to go bigger and understand GM 12v Power distribution. Inside the engine harness is this 4 wire junction.

The wires are:
#One is 12ga and comes from the battery output on the alternator. It is the only wire connected to the BAT connector on the alternator.
#Two is the alternator's voltage sensing feed. Also looks like 12ga.
#Three goes to the firewall the bulkhead connector via as PIN 2. This looks like the main power to the interior of Blazer. In think 12ga also.
#Four goes to the exposed junction block on the firewall. 12ga also? Here is a picture of that... Notice the fusible like at its end.

This distance from the 4 wire junction to the alternator (Wire one and two) is about 30 inches. Wire four is also about 30" to the expose junction block.

There is a lot going on here, but my fundamental questions is why did GM just not run the two alternator wires all the way up the harness to the exposed junction block and then distribute to the entire truck from that point? What was the thought process to only going 30 inches away from the alternator and distribute power and attach the alternator voltage sensing there?

GM has smart designers, just want to understand before I modify.

 

[K85 Octane]

Short scrap wires haha

 

[6872xtc]

One guess that I have is that they were trying to keep away from stacking terminals on the charge stud. Easier to keep corrosion to a minimum since they couldn't seal the stud up as much as wire junction. Some areas of the country have conditions that make stuff corrode just sitting, and electrical current can make it even worse. So I am guessing that they would want to increase reliability this way.
Just an idea.

 

[Wes Harden]

So have to realize that for most users the charging system and wiring where plenty in 1976. Even though extra lights then where heavy amp draws.

The bean counters, won that battle. the crimp/solder/tape splice mid loom, cost much less than more eye ring crimp/solder/tape, and the added extra wire needed for the run to the starter. Plus weight, 76 was the seconded gas shortage more people were after better mileage, and then hp ratings were falling do to to emissions. Less hp less weight.

 

[Clark75K5]

Here's more than you ever wanted to know about that splice.
Mad Electrical link

 

[snipepod]

Mad Electrical has some good info. Thanks Clark75k5. The location of the splice combined with the alternator voltage sensing is part engineering and part practical experience by the designers.

Mad Electrical talks about the usage of a HORN RELAY-with-BUS Bar. I don't think my K5 had a combo relay-bus bar, at least not that I remember. What years did the square bodies have this combo relay-bus bar?

My 76 has this which is directly fed from the 4way splice. Does this replace the combo hornrelay-bus bar that Mad Electrical references?

Cheers.

 

[Clark75K5]

MAD deals with a lot of externally- to internally- regulated alternator conversion tech, so I would assume their info provided on the horn relay is for an older vehicle, likely pre-73.

 

[Wes Harden]

I believe it is the wire with the 2 hole terminal that uses both post.

I put 1 of @$500k5 cs144 alts on my burb. Instead of replacing the battery plus wire to alt I added another, lager gauge.

 

[snipepod]

I talked with Mark from Mad Electrical. Great guy with deep knowledge.

I have a 1976 1/2 blazer. I discovered this when the 1977 wiring diagram did not match. The firewall harness plug on my K5 is the new style that continued into 1977-1979 era. Mid year 76 was the cutoff for this change. So, my K5 does not use the horn-relay as a power distribution point like earlier chevys. Instead I have the diamond shaped two stud insulated bus on the firewall. I am going to remove the 4way crimp that is buried in the harness. Then run 2 parallel 8ga wires from the alternator up the harness to one of the poles on the diamond power bus. That should be enough for my CS144 alternator.

Replace the alternator voltage remote sensor wire, to that it also goes to the diamond bus.

Replace the interior power feed so that it also attaches on the diamond bus.

The brown alternator exciter wire that runs the length of the harness, should be fine.

Down the road, I will figure out how to increase wire capacity to reach the battery.

But for the time being, I've got the main engine harness done so I can go back to body work and painting.

 

[sweetk30]

I wounder if this might be my problem on my 87 body . Lost about all real power with key on . Fuse block has good fuses . Fusible links good. Batt volt good . Grounds good .

Its this main power wire or fuse block burnt maybe . . . Just need time to tear in to it .

 

[1-ton]

Since there is no aftermarket wire harness for a 1991 V3500 chevy I had to make my own. I came across this same four wire solderless connector. Mine looked worse than yours. It was just one hunk of 1/8" thick rolled steel that was all corroded, wrapped in cloth tape, self annealing tape from the factory, and ready to crumble to pieces. I went to a electrical supply store, and got a gold plated 4-gauge solderless butt connector. I then stripped back the all the wires to clean wire, and crimped it all together. Then I put some heat shrink tubing over it, and wrapped it back in self annealing tape.

 

[eodcoduto]

Since there is no aftermarket wire harness for a 1991 V3500 chevy I had to make my own. I came across this same four wire solderless connector. Mine looked worse than yours. It was just one hunk of 1/8" thick rolled steel that was all corroded, wrapped in cloth tape, self annealing tape from the factory, and ready to crumble to pieces. I went to a electrical supply store, and got a gold plated 4-gauge solderless butt connector. I then stripped back the all the wires to clean wire, and crimped it all together. Then I put some heat shrink tubing over it, and wrapped it back in self annealing tape.

Where did you find the splice in your harness? This may be contributing to my no power issue.

 

[1-ton]

Where did you find the splice in your harness? This may be contributing to my no power issue.

It is located close to the firewall where the junction block that has the fusible link wire is for the dash wiring. I actually did not strip it back to clean wire...I installed all new 6-gauge wire instead of the factory 8-gauge wire. One problem is that the fusible link wire was replaced with 6-gauge regular wire, which could be dangerous if a short happened. I have a small roll of 8-gauge fusible link wire that I need to replace that with some day.

 

[Wes Harden]

I think you have your ga mixed up. 8 and 6 are fairly large diameters.
10 an 12 are common power feeds with 14ga fuse links.

 

[1-ton]

I think you have your ga mixed up. 8 and 6 are fairly large diameters.
10 an 12 are common power feeds with 14ga fuse links.

I think you are correct. They where factory 10-gauge, and I went to 8-gauge...Tim Allen: "more power".