1984 C20 Fuse Panel and Harness examination

[dougbert]

I have a 1984 K1500 and in dealing with the fuse panel and its wires, it is difficult locate and/or identify the wires when they are installed in the truck. Therefore I acquired a 1984 C20 fuse panel and its immediate wire harness which I can layout on a table, identify and label its wire bundles and wires.

My aim is to clean, discover and document the various wires and wire bundle on this fuse panel in order recognize the wire when looking under the dash. I don't like it when mucking with some wires that I don't know what they go to and what they are for.

So the harness came this morning, and I sprayed some ZEP 505 cleaner for it to attack the dirt on the harness and I will clean it up more in the coming days. Here are initial pictures.

Wire diagrams are located at http://www.gmsquarebody.com/forum/showthread.php?t=3834 in the electrical and audio forum. When looking at these diagrams, make sure to find the 1981 to 1987 diagrams located further down the page

Page number on the diagrams we are interested in are:

Diagram is 382 and is labeled "Typical 1981 through 1987 cab interior (1 of 2)"
Diagram is 383 and is labeled "Typical 1981 through 1987 cab interior (2 of 2)"
Diagram is 384 and is labeled "Typical 1981 through 1987 chassis and rear lighting"
Diagram is ??? and is labeled "Typical 1981 through 1987 computer control wiring system" Probably won't use this much for this thread
Diagram is ??? and is labeled "Typical 1981 through 1987 front lighting"
Diagram is 378 and is labeled "Typical 1981 through 1987 6-cylinder engine compartment". Won't use in this thread
Diagram is 380 and is labeled "Typical 1981 through 1987 instrument panel (1 of 2)"
Diagram is 381 and is labeled "Typical 1981 through 1987 instrument panel (2 of 2)"


When I first began reading these it was confusing, but with time things are getting better. One thing to note is that every wire has a number assigned to it, a CIRCUIT NUMBER and is labeled with a wire color.

There are diagrams that exist that are not in that thread. I will try to post the ones that I reference or provide links to them.
I have a Haynes Repair Manual for 1984 Pickups that has more diagrams, including more detailed ones on the actual Fuse Panel
I bought a 1984 Service manual (thick) and it has diagrams as well

Pic 1 - picture from the ebay sales post that I used here

Pic 2 - side pic of housing

Pic 3 - another side pic

Pic 4 - I believe these to be interior lighting, door switchs

Pic 5 - Head Light switch connector

 

[dougbert]

More pics

pic 1 - Instrument Panel (IP) 18 pin male plug on the left.

pic 2 - dual tank switch connector

pic 3 - don't know yet

pic 4 - side view of panel and one of the two major wire bundles coming out

pic 5 - view onto the "top" fuse side of the assembly. This is what we see when we look up on the firewall on the dash. It is composed of the fuse holder panel and is connected to the "inside" firewall bulkhead connector, with a space between them to allow wires ingress and egress. Note the silkscreen on the fuse panel which identifies what each fuse and contact point is suppose to be. NOTE: This legend applies to this particular fuse panel.

From looking at the picture, there are (top to bottom, left to right):
(---- indicates no electric connector is present in the hole)
(??? indicates no idea what that hole provides)

ROW 1:
HAZ FLASHER | CHOKE | HTR & AC

ROW 2:
HAZ FLASHER | ---- | ??? | WDO (window ??)

ROW 3:
IGN | ---- | ACCY | AUX HTR A/C | ----

ROW 4:
IGN | GAU/IDLE | RDO (radio?) | ??? | STOP HAZ

ROW 5:
IGN | T/L CTSV | WIPER | ???

ROW 6:
IGN | TURN-B/U | HORN-DIM | ECM-BAT | PWR ACCY

ROW 7:
INST LPS (lamps) | ---- | BAT | ---- | DIR-SIG FLSH

ROW 8:
LPS (Lamps) | ECM-IGN | BAT | DIR-SIG FLSH


Some holes are fuse hole with connectors while others seem to be access connectors where special connectors can be locked into place - several such wires are present in the picture

Some holes don't have connectors while some do but are not labeled nor wired

 

[HotRodPC]

This will most likely be much like the 85 and 86 harness too. 84 being the first year of the Multifunction switch on the turn signal where where bright light switch came up off the floor and the wiper switch came off the dash. In 87 TBI came about so I'd expect 87 could be a little different. Maybe not since I notice 84-86 fuse blocks have 2 ECM fuse slots. Maybe they didn't change much until 90 for the electronic speedo. Good pics and info to have for making these year model comparisons anyway if it's not the exact year model someone is working on.

I have the complete harness, every wire and all harnesses from an 81 C1500 ESC Gas engine with Auto trans and Crank Windows. Maybe I'll drag it out and do the same thing on a different thread. I'd expect it to be alot like an 81-83 harness.

 

[dougbert]

This dissection of the fuse panel and its harness will start with defining some common terminology in order to maintain some consistency within the thread and possibly with other threads.

Wiring diagrams become vital in understanding the fuse panel and the actual harness because of the labeling of circuits (by number and by color) within the harness. Therefore I will list links to wiring diagrams already located on this website and to other sources of wiring diagrams.

Wiring diagram links:

http://www.gmsquarebody.com/forum/showthread.php?t=3834

http://www.gmsquarebody.com/forum/showthread.php?t=14498

I will refer to various wiring diagrams at various times.


WARNING: Wiring diagrams cover general designs and may not be accurate for a given vehicle. For example, the wiring diagrams I have referenced for my 1984 rig, have depicted the TURN SIGNAL FLASHER in the lower right of the panel, but do not have the HAZARD FLASHER in the upper left of the panel at all. Same for this fuse panel of the C20.



First off, we will examine the actual fuse panel itself, where the fuses are inserted, etc. In referring to this panel, we need a common reference system and since the panel looks like a grid I will use grid references.

This panel grid has 8 rows and 8 columns. Rows will be labeled with a number, range 1 to 8 (top to bottom), while columns will be labeled with capital letters, A to H (left to right). In post #2 I gave a rough description of the panel's functions using row numbers but no column labels.

A "cell" will be referenced as follows: A1 to H8

Fuse positions take up 2 cells each, with a full reference of: E1-F1

Some single cells provide a "Tap" position to insert a circuit wire tap.

The flashers take up several cells.

Most cells contain a connector for grasping the tabs of fuses and wire taps. But several cells contain no connectors and are empty. These usually are taps for vehicle options that are not on this vehicle, like A/C options or power windows.

Most circuit taps are labeled by silkscreen, but a few are not labeled.



Pic 1 - Attached is a closer shot of the fuse panel.
PDF - Grid of fuse panel with identifiers

dougbert

 

[HotRodPC]

Surely GM doesn't use a different fuse block for Custom Deluxe to a Silverado would they? If so, that 84 is very different from 85 and 86. My 85 K10 Diesel Silverado has the same fuse block as my 86 C20 Gas Silverado. Very different from that 84 block you've got pictured.

 

[dougbert]

Surely GM doesn't use a different fuse block for Custom Deluxe to a Silverado would they? If so, that 84 is very different from 85 and 86. My 85 K10 Diesel Silverado has the same fuse block as my 86 C20 Gas Silverado. Very different from that 84 block you've got pictured.

I can believe such "differences"

the Ebay title for this panel was:

81 82 83 84 85 86 87 CHEVY GMC TRUCK * MAIN DASH HARNESS * C10 C20 BLAZER FUSE

Description:

MAIN DASH WIRING HARNESS
RADIO WIRES HAVE BEEN CUT

Removed from a

84 CHEVY 20

end quote

that is all I have on this critter. I have not fully compared it with my 1984 K1500. I will print out that PDF I created and take a look under the dash.

If nothing else, this thread can show the differences - eee-gags

well, I will admit I am learning to decode it. It took me awhile to see the LPS was short for LamPS and RDO is RaDiO, then T/L CTSY is Tail Light CourTeSY lights. Also learning that there are several IGN Taps. Well just in general doing this thread so far has gained myself some good insights.

dougbert

 

[chengny]

Here's how the fuse locations are layed out in a 1984 block:

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And the back side - showing the various circuit feeds in and out:

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And an actual image:

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[chengny]

The 1984 dwgs are the clearest set I have. Here are fwd lighting, V8 Eng with Light Duty Emissions & cab interior part 1 sections:

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Link to the whole 1984 C/K wiring manual on Deposit Files - 14.9 mb, zipped, no PW:


http://depositfiles.com/files/ll7qknzta

 

[HotRodPC]

Here's how the fuse locations are layed out in a 1984 block:

You must be registered for see images attach

And the back side - showing the various circuit feeds in and out:

You must be registered for see images attach

And an actual image:

You must be registered for see images attach

Well, there you go Doug. Kinda looks like Jerry saved you alot of work disecting that harness. And it does confirm you do have an 84 block. Now didn't we see an 82 block with the single flasher relay? Kinda wierd they jump back to double relay in 84, and back to single in 85 and up again.

 

[dougbert]

Took my spare panel and harness apart just a bit to see things more clearly. I found that there are two main trunk harnesses: 1 that goes up (North Harness) and 1 that goes down from the panel (South Harness)

First off

Pic 1 is a shot of various wires that were in BAT or IGN Taps, yet were cut, so I just pulled them out as I have no idea what they went to

Pic 2 - shot of the panel with the North and South harnesses clearly shown

Pic 3 - shot of the B/U lights switch connector (dark blue - power, light green - goes back to BU lights in the rear) off of the South harness

Pic 4 - next set of connectors on the South Harness

Pic 5 - end of the South harness

 

[dougbert]

There are 2 wires that are not part of the harnesses, but are single wires coming from the center of the panel/bulkhead.

1 wire is black/white strip and it has a connector that follows the driver's door. I followed it and it goes to the set of connectors ABOVE the panel with a box with tabs that plug in. My Haynes diagram call that plugin/connector the "Convenience Center" and that black/white wire is circuit 238 which is the "seat belt not fastened" alarm.

Pic 1 and Pic 2 are of that seat belt wire

Pic 3 shows that wire entering the Convenience Center socket

Pic 4 shows the Convenience Center socket and the plugin - note it has a row of 4 tabs and a row of 2 tabs center on the bottom

Pic 5 shows me re-inserting the plugin

 

[dougbert]

Pic 1 - show the Convenience Center fully installed at the top of the panel.

Pic 2 - a coil, I am not sure if it is the horn relay or a buzzer

Pic 3 - the Instrument Panel (IP) male connector on the North harness

Pic 4 - last 2 connectors on the North harness

Pic 5 - shows the circuits for the courtesy lights and door switches. The larger black block on the right is a lamp holder - I don't know if my rig has one of those, if not, I might install it

 

[dougbert]

Pic 1 - shows the dome light orange and white wires that run under the driver's side carpet and goes to the dome light and bed lamp

Pic 2 - some wire for a courtesy light (assuming since it has a white ground and brown power)

Pic 3 - Pink and black wires that go to the Dual Tank switch on the dash, and then Dark Green and Light Green wires that go from the switch back to the 6-port stepper motor

Pic 4 - more the Dual Tank wires

Pic 5 - a broken Dual Tank switch

 

[dougbert]

Pic 1 - the portion of the Dual Tank wires that go through the firewall and the connector

Pic 2 - shot of the after market Radio wires - junk as far as we are concerned

Pic 3 - shot of the door courtesy switches, one is busted up pretty good

Pic 4 - shot of the fuse panel and bulkhead connector split apart. Easy to do as there are only 2 snaps holding the two together

Pic 5 - another shot of the 2 parts.

 

[HotRodPC]

Good info. Between this and Jerry's diagrams to go with it, makes it all easy to understand.



I'm going to be cleaning up this thread to keep it 84 Specific now that we've confirmed it is in fact an 84 harness and block. I'll move those other pics and 85 diagrams I asked for out to a New thread, Fuseblock Pics and Comparisons. http://www.gmsquarebody.com/forum/showthread.php?t=18434