Need Help, Looking at one small issue lead to many.

[mclark4426]

Good morning all. This is my first topic I have posted on here. I have read hundreds of posts and you all have helped me a lot trying to get this 1985 GMC Sierra on the road. I thank all of you for that!

First, I have 85 GMC Sierra, High Sierra model. Rebuilt 350 on an 1988 3500 block with mostly edelbrock parts, including an Edelbrock carb. 700R4 tranny that was rebuilt last year. I would like to take out all the wires that I don't need and make sure it's wired correctly. I have looked at the wiring diagrams many times on this site with little help. It appears I don't understand a lot of it.

 I started with the temp gauge(it was pegging hot), first I replaced the gauge to clean up the gauge cluster. The cluster has been completely rebuilt. Starting with gauge cluster backing plate, printed circuit, and all the clips were cleaned that hold on the printed circuit. I installed a temp sensor in the thermostat housing. I traced the green wire from the new gauge, thru to the back of the bulkhead. Out the other side and to the new sensor, no breaks in the wire. It moved to the left side of the gauge, around 100 degrees. I drove it down the road and around 4 miles down the road it went and pegged hot again. Did some more research on this forum and someone mentioned it could have gotten hot on the valve cover and grounding out. I put the wire in a loom and it seems to stay at 100. Never moves.

The oil pressure sensor also is pegged hot. Their isn't a tan wire coming out of the bulkhead to go to sensor. I traced it back from the gauge cluster to the bulkhead and it's complete with no breaks. Problem is, I don't know where to put the wire in the bulkhead. I'm pretty sure if I take down my fuse box I could figure it out but, I would rather not get into that if I can help it. I did some research and it appears that the white wire from my alternator is in the spot the brown wire should be coming out of the bulkhead. Where should that tan wire for the oil pressure gauge go? Where should the wire wire from the clip on the alternator go? Does anyone have a picture a the bulkhead to show where all the wires should be?

I also have wires going to connectors that aren't plugged in. Can I remove them? The wire that goes to the AC compressor has two clips in the line between the compressor and relay, can that be correct?

[Rapid Roy]

Welcome

[mclark4426]

Thank you!

[bd]

That isn't a GM sensor in the thermostat housing.  Is it connected to a factory gauge?  Why are two wires (red and white) connected to the temperature sender?  If the temp gauge "never" varies from 100°F, it may be an incompatibility between the sensor and the gauge and/or may be wired incorrectly.

Post a pic of the bulkhead connector protruding from the firewall so we can clearly see which cavities are populated by terminals, then reassemble the bulkhead plug.  Clip an incandescent test light to a verified good ground.  With the ignition switched on, probe the cavity labeled "OIL PRESSURE TAN (?)" in the attached image while an assistant monitors the oil pressure gauge.  Does the gauge needle move at all? 

What is the alternator's output rating and what is the reason behind the split insulation and bare wire connected to the B+ post at the back of the alternator?  The wire appears undersized for a charge lead.  Is there a hidden, larger gauge wire connected to the B+ post in addition to the one visible in the image?  In addition, that isn't the original two-wire connector plugged into the regulator.  You need to determine exactly where each wire runs and connects.  There is something suspect going on there that may be a fire waiting to ignite.

The factory A/C compressor harness contains two wires.  One is dark green and runs to the compressor clutch.  The other is light green that ran to a fast idle solenoid on the original carburetor.  An additional, typically short black wire runs between the factory compressor clutch and ground.  The factory compressor is cycled on and off by a pressure switch located on the accumulator.  There is no relay.  I assume when you are referencing "clips," you actually mean connectors.  The original A/C compressor harness contains at least three connectors.

[mclark4426]

Thanks for responding BD, I was hoping you would. The white wire on the temp sensor is gray. It's part of the relay system I just installed for electric fans on the radiator I haven't installed yet. That is another issue I am working on. I thought, maybe, that the gray wire was causing an issue with it being installed with none of the other wires from that relay system installed but, I have received the same result both ways. I can remove the gray wire if you need me to.

I don't own a test light, I'll try to run in the morning and get one.

I have no doubt the wire from the alternator is under sized. I don't trust that the previous owner did this correctly and this is the first time I have tried to figure out the wiring in this truck. It appears it's a huge mess. The alternator output is 105 amps. I added pictures on where the 3 alternator wires go. They are the first 3 pictures.

I also added a picture of the wires that go to the pressure clutch. The two connectors that are connected in line with the ac are supposed to be there? I have to make these pictures really small, I hope they work for you.

[bd]

Are you installing a Dakota Digital fan controller?  I recommend that you dedicate the T-stat sender to the fan controller.  Install the correct OEM temperature sender in the left cylinder head for the dash temperature gauge.

When purchasing a test light, procure one with an incandescent bulb.  The reason for incandescent is that it slightly loads a circuit and makes voltage losses through unwanted resistances more readily apparent.

The alternator B+ lead should be replaced with an 8-gauge (or 6-gauge) charge lead that connects directly to the battery positive post through a 6" long, 12-gauge (or 10-gauge, respectively) fusible link.  See How to make a Fusible Link in the Technical Forum for details, if necessary.  Mechanically crimp and then solder the wire terminals and splices using 60/40 rosin core solder.  Shrink seal the wire-to-terminal joints using marine grade, adhesive lined, dual-wall, polyolefin shrink.  Eliminate the existing charge lead that runs between the B+ post of the alternator and the firewall junction block. 

The 14-gauge red wire from the two-wire regulator connector (following image) should jumper directly to the B+ post of the alternator.  If the red wire is too short to reach, purchase a new regulator pigtail from your local auto parts store. 




The 18-gauge white wire from the regulator connector (previous image) should splice into a brown single strand resistance wire that runs to the firewall bulkhead connector (following image).




The A/C low-pressure cycling switch threads into the cylindrical aluminum accumulator located in front of the evaporator housing (following image).  Note the light green and dark green wires that are attached to the switch...




It appears that the two green wires originally connected to the cycling switch were severed and removed by the PO (image below).  I noticed earlier in the thread that the compressor has been replaced.  Did the PO convert other components of the A/C system as well?  Perhaps you should post images that more fully show the major under hood components of the A/C system, including the specific connectors that you keep asking about.




Compare the wire colors in the subsequent image to those in the previous image.  See any similarity?




The clear picture of the bulkhead connector that I requested earlier should be clarified in the image below.  Bear in mind that I need to be able to determine which cavities are populated by wire terminals.

[mclark4426]

Good morning, i installed this relay kit.

https://www.amazon.com/gp/product/B07143JTWM/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

I'll make that wire today that goes from the battery to the alternator and replace the connector. The wire in that connector at the alternator has a bar wire showing. The white wire from the alternator does splice into a brown wire and go to the bulkhead where you labeled it.

I took a picture of the cable from the battery and where they go. I have a 6 gauge wire going from the battery to the starter, is that supposed to be there? I marked the other two as well.

As for the AC. The light green wire from the pressure switch goes into the firewall just right of the evaporator core (looking from the front bumper into the engine bay). The dark green wire goes over to the compressor that was shown in a previous picture.

The wires in the last two pictures you posted look the same to me. Looks like they go into the fire wall just right of the evaporator and they come back out under the bulkhead. I don't have anywhere to connect them to. I'm guessing I have a missing connector near the compressor somewhere?

I added pictures of the engine bay so you can see the other components. I changed out the compressor, evaporator core, accumulator, and pressure switch. The AC system worked last summer before I sent it to get painted and the engine rebuilt. It came back not working. 

[mclark4426]

I got a test light and notated what I found on the picture. The choke indicator light wire, does that need to be connected to the electric choke somewhere on the carb?

I would like to hook up the pressure switch to the original wires if possible. What does the stock connector look like on the compressor end?

[mclark4426]

Looking at the diagram, I believe both of the smaller gauge wires coming off the battery should have fusable links on them and they should be attached at the starter. If that's correct, what gauge wire should the 2 wires coming off the starter be?

[bd]

The challenge of preexisting wire alterations is to figure out what the "other guy" did....  It seems you are progressing nicely.  So, well done!

You definitely need to connect your dash gauge to a dedicated temp sender mounted in the OE location (left cylinder head).

How many wires attach to the starter solenoid?  Post a pic.  The B+ battery cable to the starter solenoid should be stranded copper, 4-gauge minimum (2-gauge optimum), SGX cable.  Be sure to route the cable safely away from exhaust heat and clamp the cable to keep it stationary and positioned so that it cannot chafe to ground as it transitions from frame-to-engine, passing the engine mount.  Allow sufficient slack for engine movement since the engine mounts are not rigid.



I suspect that the two red wires connected to battery B+ originally connected to the starter solenoid 3/8" battery cable stud.  They can remain connected to the battery or be relocated to the starter as you prefer.  However, they should be protected by one shared or two independent fusible links that are four wire gauges numerically larger than the wires they protect (e.g., if the two red wires are 12 gauge, the fusible link(s) should be 16 gauge).  Preferentially upgrade the wire that feeds the firewall junction block to 10-gauge SXL or GXL protected by a 14-gauge fusible link.  This will compensate for the additional length of wire run to the battery if you decide to retain the present configuration while allowing greater flexibility for adding electrical options in the future.  To state the obvious, if you elect to upgrade the wire as suggested, replace the entire length of wire between the battery and junction block.  Do not splice into any existing wire(s).

Look closely at the blower resistor wiring and "unknown" wire connector previously imaged and discussed.  I don't believe they are related.  You may need to trace the "unknown" to see where the opposite end connects.

Regarding the A/C wiring, study the diagram below.  I added color and simplified the annotation to help you interpret and compare the diagram to your vehicle.     Pay attention to the green wires and where they connect as delivered from the factory.  Note that the idle solenoid is optional, but can significantly improve idle quality on engines with carburetors that are conducive to mounting.  Since the A/C worked as reconfigured, I recommend a thorough survey of what was altered before changing or reverting anything.  FYI - The connector plugged into the new compressor pigtail is the stock connector that mated to the original compressor.

To restore the dash choke light operation review GM Electric Choke Operation and mimic the wiring.  You will need to procure and install an appropriate OPS either adjacent to the distributor if there is sufficient space or down by the oil filter and run wires accordingly.

At some point you will need to reloom the engine harness to organize it and provide some protection.  Plan wire routing now so that when stringing new wire it will fit into the future loom and drop out where you want it rather than awkwardly.

You should consider looming the spark plug wires too to prevent physical damage to the wires, arcing or cross-firing between cylinders.  Headers radiate extreme heat during engine loading because there is insufficient mass to sink and buffer the exhaust heat.  Often, the penalty is heat damage to the spark plug boots, arcing and misfire once insulation breaks down or the cable cores burn back inside their jackets.  Consider Kevlar or Nomex heat socks for the spark plug ends of the cables in addition to the cable looms.

[mclark4426]

Thank you for your help, guys like you are the reason guys like me don't burn down their trucks!

I attached a picture of the starter, only the wire from the battery (looks like this wire is actually 2 gauge, not 6 gauge like I originally thought) and a wire going to the bulkhead. I'll move both wires from the battery to the starter.  Should they both be 10 gauge? I think the shorter length from the starter to the bulkhead and junction block will help and it will cut down on all the wires going to the battery. Plus, it will allow me to change the gauge of the wire to 10 gauge like you mentioned. I'll add fusible links to both wires instead of combining them into one.

Ill get the proper temp sensor tomorrow and install it in the block and move the gray wire to that sensor.

I'll finish tracing the unknown wires. They go into the dash, under the bulkhead and travel somewhere behind the temp controls on the dash. I would like to reconnect the original wires to the pressure switch and determine where the original locations were. It appears they are cut on both ends on my truck.

My spark plug wires were tied out of the way with most of the wire mess I have but, i cut it to trace wires and to get a better look around. I have the spark plug wire looms sitting on the bench but, that job keeps getting pushed back for more important issues. First it was ball joints, tie rods, and steering gear (that is sitting on the bench), then that got pushed by the temp sensor and the radiator replacement. All that was then pushed to figure out these current issues.

I don't recall an idle solenoid on the old carb and i'm not sure where that would go.

I was going to ask you about the boots, thank you for being a step ahead! What wire loom do you prefer?

[mclark4426]

Is there a location I can find what all the original wire gauges were? Figured that would be easier than asking every time... 

[bd]

You're going to run out of bench space if you're not careful.   

Much of the information you're requesting (wire sizes, colors, etc) is in the 1985 Wiring Manual.  The wire gauges are listed on the diagram in their metric equivalents so you will need to refer to the conversion chart on page 3 of the manual.

Wire codes explained:  3 RED-2  means the wire has 3 (mm)² of cross-sectional area, it has red insulation and the circuit number is 2.  3 (mm)² is the metric equivalent of 12 gauge.  Generally speaking, OEM wire uses SXL insulation due to its superior ozone and temperature tolerances.

Referring to the latest image, the battery cable rests uncomfortably close to the lower starter motor lug of the solenoid.  You should increase the spacing or form a 90° bend in the terminal end of the cable.

The original red wire running between the starter solenoid B+ stud and firewall bulkhead connector was 12 gauge protected by a 16-gauge link.  I stand corrected on the OE red wire running to the junction block - it was originally 10 gauge protected by a 14-gauge link.  You can maintain the original wire sizes in both cases.

Possibilities:

Loom

Boots

[mclark4426]

I was hoping these "needed" projects were going to slow down!

I was curious what the 3 red-2 meant. Glad I asked! Thanks, I'll move the battery cable. Looks like I have a lot of work to do when I get out of work tomorrow...

[bd]

Regarding a protective covering for the primary wiring, I prefer high-temperature nylon, convoluted split loom.  It is durable and withstands working temperature up to 300° F.