Cab wiring problems

[wileecoyote427]

I have an 84 c30 was a dump truck in a former life now sports a home grown flatbed. Have some issues with the lighting and electrical isn’t my thing it has no interior lights 2 sets of wires looped together I assume one is the clutch safety switch the burned spot on the fuse block is where a flasher is at not sure what got it so hot that it did that the solid green one that looks burnt and the brown and yella wire looped are for I have a factory 84 service manual but it’s not the greatest trying to read the wiring layout

[hatzie]

The Purple to Yellow is Neutral-Safety or Clutch interlock starter interrupt wiring.

That flasher relay socket took some abuse. Probably the terminals got loose on the flasher relay and heated up from arcing between the male flasher terminal and the female harness terminal. Someone has gotten after the terminal in the melted socket with lord knows what in an abortive attempt to remove it. That socket is probably toast.
Dorman makes a two wire flasher socket with a pigtail. Look for Dorman 84734. You could solder and heatshrink the Dorman repair pigtail wires to your flasher wires and carefully screw a flasher relay mounting bracket to the now dead and empty flasher socket.

[hatzie]

The crispy light green wire in the picture with the starter interlock bypass is probably the backup lamp filament power. I don't see the dark blue wire that actually provides ignition power to the backup lamp switch.

Yellow and Tan... what sockets are these near.
Can you buzz em out to a bulkhead plug terminal or fuse panel terminal with a Meter or fox and hound??

BTW the 1984 wiring manual is in the 1973-1991 manuals link.

[wileecoyote427]

With the harness in the truck the tan and yella wires would close to the steering column and the length of the burnt green one falls close to them. I’ll assume this is the blue and green wire for back up lights you are talking about. Part numbers are good to fix it right they had that flasher just hanging in the air

[hatzie]

Well. That helps a great deal. That black two position plug is likely the backup lamps.

If you look at the 1984 wiring diagrams near the lower left corner of PDF page 10 you'll see that the DIMMER SWITCH has Yellow, TAN, and LT-Green wires. Looks like the terminals will need to be replaced. The terminal on the green wire is pretty crispy and I bet the Yellow and TAN terminals are just as bad or just plain missing.

The missing connector you're looking for is Delphi Packard 8917693. This Packard 56 series plug was superseded by PN 12102757. This connector was used on the 84-91 squares and the early T400 platform trucks along a lot of 80's and early 1990's GM cars (B & G body for sure). You can buy 12102757 as a pigtail on Amazon or RockAuto or...
https://www.amazon.com/Headlight-Dim.../dp/B0040D2OHA
http://www.rockauto.com/en/catalog/c...connector,2572


The easiest and least expensive way to fix it is to solder the service pigtail wires to the Yellow/Tan/LT-Green wires and cover each splice with adhesive heatshrink that extends 2-3" up the jacket of each wire.

Cleaner looking, and also more time consuming and expensive, would be to install new terminals on the harness wires, extract the pigtail wires from the new shell, and insert the harness wires in the proper cavities of the new plug.

Female Packard 56/59 connectors are very easy to extract with a thin shank #0 precision flat blade screwdriver. The rectangular hole for the mating male terminal blade has a small square bump-out to insert the extractor.
The top view of this Female Packard 56 terminal shows the retention tang you'll be pushing down to extract the terminal from the connector. I usually push the wire into the connector then insert the extractor and pull back on the wire.


Looking at the 1984 wiring diagrams we can see the Yellow and LT-Green wires are 1mm² (16AWG) and the TAN wire is .8mm² (18AWG).
You'll need two Delphi 56 series 2965687 14-16 Gauge Female and one 2965510 18 Gauge Female
You can get Packard 56 terminals and Delphi tooling from TheElectricalDepot in convenient small project quantities for a pretty decent price and no minimum order. It's a small operation but they're good people.

Mouser Electronics has an absolutely massive selection of Delphi terminals and connector shells and tooling for pretty reasonable prices but they have minimum dollar and quantity amounts for orders.

[wileecoyote427]

Awesome I appreciate the help got me squared away for now while I order these parts up and then see what else isn’t working.

[wileecoyote427]

Ordered up parts to fix the few issues covered already the wiring showed up waiting for the new dimmer switch. While I was at it figured why not spring for all new battery cables clean up the mess of bolts with nuts used to tighten them that was on here all new acdelco parts negative cables are fine no problems but the positive cables don’t fit from one side is fine the battery to battery and battery to starter is wrong they sent me all negative covers which I can live with if they actually would have fit is there any place to buy the positive covers or am I stuck with bare connections on the battery to battery

[hatzie]

I'm not a fan of the side terminal batteries. I installed a pair of siamese ( the + lugs are on LH & RH sides to put them close to the middle ) HD 78 series top terminal batteries in my 76 to turn the starter on my 6.5L.

I got a hydraulic battery lug crimper and bought too-long cables with cast-on top-terminal lugs. I cut em to fit and then hex crimped the correct hole size ring terminals. I fill the terminal with Copper no-ox paste before I insert the wire and cover the crimped connector with adhesive heat shrink @ 1.5" up the cable. I've used the crimper several times for other projects like the winch cables on my families' ATV fleet and the plow trucks.

The original Positive cable is a single BLACK wire direct to the BAT terminal on the starter with no branches and a red shroud on the positive terminal.
The Ground cable is the one with a 12 ga branch wire to the radiator shroud. The heavy cable runs directly to the alternator bracket. I usually forego the extra wire and get heavy braided jumpers that I soak in oil and run from the block to the frame and the cab on both sides of the engine. I also tie the rad shroud to the frame on both sides and the fenders to the rad shroud as close to the corners as possible. Tying the body and the frame together electrically as much as possible cuts down on corrosion at the seams and connection points like the bed bolts.

To add to the confusion the OEM diesel twin battery setups used a RED cable with red ends from battery to battery...

American Auto Wire and Classic Industries sell red and black side and top terminal shrouds, side lug battery bolts, and "W" crimp side battery terminals as a kit. There are more just google it. You should be able to buy a set of those and just pitch the ring terminals in the top of your toolbox.

[wileecoyote427]

I only went with new it was easier and they weren’t terribly expensive and were here in 2 days with amazon prime. This is actually a 6.2 truck and turns out there is a spacer I’m missing for the positive cables took some searching and just the right words but it’s one more piece of the wiring nightmare down. I do appreciate the other info will be helpful with the wiring on my other truck when I get to it.

[hatzie]

Yup The diesel positive cables have a spacer and a longer bolt.

The ground from the LH battery runs to the engine. I don't remember where.

[wileecoyote427]

Yeah came with the long bolt but the spacer is missing they had all the rubbers ripped off and bolts with nuts to keep everything tight and I’m guessing they were the original ones. Yeah it was grounded to an intake bolt.

[hatzie]

Originally Posted by wileecoyote427

Yeah came with the long bolt but the spacer is missing they had all the rubbers ripped off and bolts with nuts to keep everything tight and I’m guessing they were the original ones. Yeah it was grounded to an intake bolt.

The stock setup on my 2000 had two lugs under one cover. If you have access to a lathe just turn a brass slug to fit the situation.

[wileecoyote427]

I wish I had a lathe. Between the being to cold for me wanting to go outside and the snow that rolled through after new year I finally got the right parts soldered the new dimmer switch on wrapped everything cleaned it up. I have a ground wire that’s been cut on the section of the harness with the light switch plug cluster plug. And on the end of the headlight switch plug is another ground wire that was hooked up to a wire running up to the cab lights I don’t see anywhere else that the wire would go to and in the book the spot where the black wire is on the plug is labeled 9 but goes nowhere in the diagram but it does light up the cab lights. If I touch the cut ground wire to the dash it makes the fuel gauge and temp gauge move and the driver side blinker will light up and with not touching the wire the passenger blinker is the only light lit

[hatzie]

You mention "Cab Lights"... Cab Clearance Lights on the front edge of the roof? GM calls them Roof Marker Lights RPO U01. You'll find the diagram in the lower RH corner of Page 1E. These should be grounded to the sheet metal of the roof and they should get POWER from the Headlight Switch Terminal 3 Circuit 9 ( the socket with the dashed line next to it on Page 1A ).

The numbers in the plug drawing are GM circuit numbers. If you look to the right of the switch drawing you'll see a list of numbers and functions.

Circuit 9 is TAIL LP...

If you look at the pages immediately preceding the first foldout diagram you'll find GM circuit tables with a wealth of detailed information.
The first column is Circuit Number then Circuit Color (wire color), then Circuit Name (description).

Circuit 9 says it's a BROWN wire for the "Tail, License, Park and Side Marker Lamp Feed" Roof Marker lights fall into the marker lamp category and this is definitely a POWER wire not a ground wire.

Black is usually Circuit 150 which is a ground. Sounds like the previous owner might've done some repairs with whatever color wire was at hand. You need to do some detective work. I'd chase that black wire and find where both ends live. If you have a Fox and Hound it may make it easier. Then I'd look in the circuit tables for the original wire color and GM circuit number that GM used for the function you discovered. Then you can find it in the diagrams.

As you proceed you'll be able to read the diagrams more and more easily. If you want a good scare take a look at the 1987 Light Truck wiring book in my signature. It's an abomination. I've learned to read the 87 diagrams but they are really miserable. Apparently GM got some really bad feedback from Mr Goodwrench because 1988 is actually readable again.

[wileecoyote427]

Ok so that confirms the roof lamps with the plug on the headlamp switch it says 9 brown but looks black to me.

Now the ground wire I’m trying to chase is a factory splice spot and has 7 wires running in and out of it everything seems to be running where it needs to be with the exception of the cut ground. Could the plug have been cut and it actually goes to the glow plug/water in fuel lights. Or do they plug into the 6 pin block above the parking brake? That’s the only wire I have left on this section of the harness and with the exception of the button for the glow plugs needing cleaned up the engine harness doesn’t look to have been butchered.

[hatzie]

At least one wire from Splice 150 should go to the Ground buss bar above the E-Brake Pedal. If you don't have one then it's probably what got cut off.

GM used a ring terminal on the bolt connecting the buss bar to the kick panel sheet metal according to the diagrams.

Some possibly helpful trivia on the diagrams...

Notice the Delphi connector shell part numbers for each and every electrical connector are right next to the terminal in the drawings?

This is how you can tell from the above section that the Tach and Clock used Delphi 12004267 Packard 56 connector shells to connect to the ground buss bar. Looking up the connector shell online will tell you what family they belong to and from there you can find the terminals to crimp onto the wire. Mouser Electronics has a lot of Delphi connectors listed even if they don't stock them. They also usually have links to available data-sheets.
GM bought into the whole "were going Metric thing" so the conductor diameter isn't listed in AWG on the GM wiring diagrams after 1978 or 1979.
Just before the wire color circuit number tables you'll find a mm² to AWG table.
The conductor diameter is called out in mm² immediately preceding the wire color which is followed by a dash and then the circuit number. The ground circuit you're chasing says .8 BLK-150 Translated---> .8mm² (18AWG) BLK (BLACK) - Circuit 150 (Ground).

[wileecoyote427]

Ok so a ring terminal in the center. And I’m guessing I can plug the ground from the glow/water lights onto that buss bar. And that should clear up all the wiring.

Yeah that’s extremely helpful didn’t even pay attention to the smaller numbers trying to follow the wires everywhere.

[hatzie]

Originally Posted by wileecoyote427

Ok so a ring terminal in the center. And I’m guessing I can plug the ground from the glow/water lights onto that buss bar. And that should clear up all the wiring.

Look at the Diesel diagram in the left hand pane of Page 1B. That's exactly where GM terminated Circuit 150 feeding the Glow Plug Lamp and the Low Coolant Switching Module. The Low Coolant and Water IN Fuel lamps are not directly grounded to the chassis.

If you look closely at the Diesel wiring diagram it shows that both the Pressure Sensor and Water IN Fuel Sensor in the Stanadyne 80 fuel filter head feed the Water IN Fuel Bulb. I never had a factory Squarebody diesel so I didn't realize how that worked. My 76 has a 6.5L with the top loading Stanadyne 29367 Fuel Filter Manager in the intake valley just like it was in the T400 donor truck. I just wired up a WIF lamp to the WIF sensor and left it at that.

Originally Posted by wileecoyote427

Yeah that’s extremely helpful didn’t even pay attention to the smaller numbers trying to follow the wires everywhere.

It took me a while to figure out what they were. Darn handy once you know.

[wileecoyote427]

Hatzie You’ve been extremely helpful with this got everything hooked back up a fuel gauge that moves now a blinker lights up and a glow plug light that’s touchy with a loose ground in the plug but no dash lights or gauge movement even the hvac light won’t light.

[hatzie]

As long as your grounds at Splice 150 are connected to the ground bar with one of the wires at that splice then it's in the power side of the circuit.

The dash/radio/HVAC lamps that dim as you turn the headlamp knob are on Circuit 8.
The Dark Green Circuit 44 wire off the headlamp switch dimmer rheostat on page 1B feeds the INST LPS fuse on page 1A.
The INST LPS fuse feeds the Gray Circuit 8 wire that's spliced (Splice 8) to four Gray wires... the Instrument panel plug, the HVAC lamp, the Seatbelt timer, and the Radio dial lamp.

If the Glow plug ground is loose at the buss bar it can be repaired with a new Packard 56 Female terminal using the original plastic shell. Or you can use Panduit or Noble 1/4 disconnect terminals. The Borg store terminals will loosen up on the wire and the buss bar fairly shortly because the metal is not the right alloy to retain its' shape long term.
The lamp socket is a bit more of an adventure to repair.

[wileecoyote427]

Got the lights to work ended up with a bad headlight switch switched it out with another one I had laying aroundI’m not that lucky it’s loose at the bulb end.
So thanks for all the help with getting this cleared up.

Volt water and oil gauges haven’t worked with it running and idling and since everything looks original under the hood figure new senders wouldn’t hurt.

[hatzie]

The volt gauge just needs power and ground at the cluster plug through the printed circuit.

If all of the cluster illumination lights work the volt gauge ground is ok.
The turn, brake, seatbelt bulbs share grounds with oil & temp gauges so if they work this ground is ok.

Check the PINK/BLACK power wires. One of them feed the volts another feeds the temp, and oil gauges. The third is for the fuel gauge and also feeds the BRAKE lamp.

[wileecoyote427]

Yeah all but I think one bulb is lit. Turn signals don’t light up no parking brake light and seatbelt wire was cut. I checked the pink/black wires on the cluster plug with a test light they all lit up. The low coolant light is is off a pink/black wire but it’s gotta becmoved just right and it flashes really quick but won’t stay lit. I tried a different cluster from a gas truck just to see what happend and still had nothing thought the printed circuit wasn’t the best looking so it was worth a shot